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ABSTRACT
THE EVALUATION OF PLANT GROWTH REGULATORS ON SCARLET ROYAL TABLE GRAPES TO DETERMINE POST
HARVEST QUALITY
The incidence of Botrytis cinerea and other diseases as well as berry quality
parameters were evaluated on Scarlet Royal after post-harvest storage using
different combinations of plant growth regulators (PGR) during the growing
season. Three treatments including a Control (no PGR applied), 5 ppm
Gibberellic Acid (GA3) and a combination of 5 ppm GA3 + 6 ppm
Forchlorfenuron (CPPU) were applied. After commercial cold storage was
completed, berries were evaluated for Botrytis bunch rot, berry crack, berry
shatter, other diseases and other damage. Normal berry quality parameters were
also evaluated including pH, titratable acidity, total soluble solids, berry
firmness, berry diameter, berry length and skin color.
Results showed no significant differences for Botrytis bunch rot incidence,
berry crack, other diseases or other damage. However, berry shatter was
significantly higher for the 5 ppm GA3 treatment. The three treatments showed
no effect on berry firmness, berry diameter, berry length, juice pH, titratable
acidity and total soluble solids. Furthermore, berry color presented no
differences in lightness, chroma or hue.
Victoria Towers May 2015
THE EVALUATION OF PLANT GROWTH REGULATORS ON
SCARLET ROYAL TABLE GRAPES TO DETERMINE POST
HARVEST QUALITY
by
Victoria Towers
A thesis
submitted in partial
fulfillment of the requirements for the degree of
Master of Science in Viticulture and Enology
in the Jordan College of Agricultural Sciences and Technology
California State University, Fresno
May 2015
APPROVED
For the Department of Viticulture and Enology:
We, the undersigned, certify that the thesis of the following student meets the required standards of scholarship, format, and style of the university and the student's graduate degree program for the awarding of the master's degree. Victoria Towers
Thesis Author
Sonet Van Zyl (Chair) Viticulture and Enology
Kaan Kurtural Viticulture and Enology
Anil Shrestha Plant Science
For the University Graduate Committee:
Dean, Division of Graduate Studies
AUTHORIZATION FOR REPRODUCTION
OF MASTER’S THESIS
X I grant permission for the reproduction of this thesis in part or
in its entirety without further authorization from me, on the
condition that the person or agency requesting reproduction
absorbs the cost and provides proper acknowledgment of
authorship.
Permission to reproduce this thesis in part or in its entirety must
be obtained from me.
Signature of thesis author:
ACKNOWLEDGMENTS
I would like to express my most sincere gratitude to the members of my
committee Dr. Kaan Kurtural and Dr. Anil Shrestha for their help and guidance
and in particular to my adviser Dr. Sonet Van Zyl for giving me the opportunity
to work with her, for her guidance and her friendship. I would also like to extend
my gratitude to The California State University Agricultural Research Institute
and The California Table Grape Commission for their financial support for this
project and to Scatagglia Growers and Shippers for providing the vineyard as
well as their cold storage facilities and staff. I would particularly want to thank
Craig Calandra, Vincent Silva and Darryl Alchian for their help, expertise and
patience in the field. Others who are appreciated for their hard work and sincere
friendship are my coworkers and lab team Amanda Burke, Laura Richaud, Erin
Palumbo, Thomas Duvall, Humberto Topete, Alexander Pineda and Jaqueline
Chenoweth.
Finally, I would like to express my gratitude to my family and friends for
their support and encouragement throughout my time at Fresno State without
whom I would not have received this degree.
Thank you.
TABLE OF CONTENTS
Page
LIST OF TABLES ............................................................................................................ vii
LIST OF FIGURES ......................................................................................................... viii
CHAPTER 1: INTRODUCTION .................................................................................... 1
CHAPTER 2: LITERATURE REVIEW .......................................................................... 3
Table Grapes: Importance and Production in the World and the United States .............................................................................................................. 3
Fresno County Climate ........................................................................................... 5
Scarlet Royal Table Gapes ....................................................................................... 8
Production Problems and Special Considerations for Scarlet Royal .............. 10
Pre and Post-Harvest Pathological Problems in Table Grapes ...................... 10
Plant Growth Regulators: Gibberellins and Cytokinins ................................... 25
Cluster and Berry Thinning .................................................................................. 33
CHAPTER 3: MATERIALS AND METHODS ........................................................... 36
Site Selection ........................................................................................................... 36
Experimental Design ............................................................................................. 36
Treatment Applications ......................................................................................... 36
Post-Harvest Decay Forecasting .......................................................................... 37
Parameters Measured and Instruments Used .................................................... 38
Statistical Analysis ................................................................................................. 40
CHAPTER 4: RESULTS AND DISCUSSION ............................................................. 41
Post-Harvest Decay Forecasting .......................................................................... 41
Experimental Results ............................................................................................. 43
Discussion ............................................................................................................... 45
CHAPTER 5: CONCLUSION ....................................................................................... 48
Page
vi vi
REFERENCES ................................................................................................................. 49
APPENDIX: TABLE GRAPE TYPES: SURFACE AREA IN HECTARES BY VARIETY AND YEAR PLANTED IN CALIFORNIA .................................. 57
LIST OF TABLES
Page
Table 1: Acreage Standing by County and Year Planted in California for Table Grapes (CDFA, 2014). ............................................................................. 4
Table 2: Cultural Practices for Scarlet Royal Table Grapes. ....................................... 9
Table 3: Fungicide Efficacy for Botrytis and Summer Bunch Rot Control (Adaskaveg et al., 2013). ................................................................................. 18
Table 4: Treatments, Concentration Rates and Commercial Product .................... 37
Table 5: Percentage of Botrytis cinerea and Other Diseases Affecting Control, GA3 Treatment and GA3+CPPU Treatment in 2013 and 2014. .................. 41
Table 6: Effect of GA3 and GA3+CPPU on Percentage of Botrytis cinerea Incidence, Berry Shatter, Berry Crack, Other Damage and Other Disease Incidence at Post-Harvest on Scarlet Royal Table Grapes .......... 43
Table 7: Effect of GA3 and GA3+CPPU on Berry Length, Berry Width, Berry Firmness and Berry Color (Lightness, Chroma and Hue) at Post-Harvest on Scarlet Royal Table Grapes. ....................................................... 44
Table 8: Effect of GA3 and GA3+CPPU on Berry Juice pH, Titratable Acidity and Total Soluble Solids at Post-Harvest on Scarlet Royal Table Grapes. .............................................................................................................. 45
LIST OF FIGURES
Page
Figure 1: Average Temperature from 1971-2007. Adapted from Annual Climatology: Fresno, CA (Fresno County, 2014) and The Weather Channel: Monthly Weather for Fresno (The Weather Channel, 2014). Accessed 02/2014. ................................................................................. 6
Figure 2: Average Precipitation from 1971-2007. Adapted from Annual Climatology: Fresno, CA (Fresno County, 2014) and The Weather Channel: Monthly Weather for Fresno (The Weather Channel, 2014). Accessed 02/2014. ................................................................................. 7
Figure 3: Calendar of Weather Events for the Southern San Joaquin Valley (Vasquez et al., 2013). ...................................................................................... 8
Figure 4: Botrytis cinerea life cycle (Marois et al., 1992). ............................................ 13
Figure 5: Grapes Arranged for Post-Harvest Decay Forecasting Showing Infected Berries. ............................................................................................. 42
Figure 6: From Left to Right: Botrytis Infected Berry, Penicillium Infected Berry, Cladosporium Infected Berry and Aspergillus Infected Berry. ....... 42
CHAPTER 1: INTRODUCTION
The total table grape production in the world currently exceeds 18.1
million tons per year. China is the leading table grape producer followed by
Turkey and the European Union. According to the United States Department of
Agriculture (USDA) the United States is the 6th largest producer with a total of
1,017,000 tons for the 2013/14 season (USDA, 2014a).
The total world trade for fresh table grapes is around 2.5 million tons a
year. Chile and the United States are the main table grape exporters with 755,000
and 416,000 tons per year, respectively (USDA, 2014a).
The California Table Grape Commission (CTGC) reported that table
grapes are one of the preferred fresh fruits consumed in the United States along
with bananas and apples with a mean consumption of 3.52 kg per capita per year
(USDA, 2014b).
Of the commercial fresh grapes grown in the United States, California
produces 99% (CTGC, 2013) with a total of 36,912 ha. California exports 41% of
the total production as fresh fruit to over 50 overseas markets, and according to
the California Department of Food and Agriculture this represents a total of 812.3
million USD per year (CDFA, 2013a; USDA, 2014a).
Botrytis cinerea causes the fungal disease known as gray mold. It is
considered the most damaging disease in table grapes since it can infect the
berries in the field and continue its development during cold storage (Gubler et
al., 2006). This fungus can affect the entire vine including succulent tissue and
stressed or dead tissue. The most susceptible cultivars generally present a
vigorous canopy, tightly arranged clusters and thin-skinned berries. The
susceptibility increases when growing conditions are humid (Bettiga and Gubler,
2013).
2 2
Gray mold can be controlled in the vineyard and during post-harvest by
applying an integrated approach. This approach considers the combination of
different practices such as chemical control, vineyard sanitation, canopy
management, irrigation management, berry damage reduction practices and
plant resistance (Bettiga and Gubler, 2013).
Plant growth regulators (PGR) such as Gibberellic Acid (GA3) and
Forchlorfenuron (CPPU) are usually applied to table grapes at several growth
stages at different concentrations with the main purpose of reducing fruit set and
increasing berry size (Christodoulou et al., 1968). These applications also have an
effect on cluster tightness, berry skin thickness and pedicel rigidity which in
combination affects susceptibility to disease infection and storage potential of the
harvested fruit (Ben-Arie et al., 1998)
The main objective of this research project was to evaluate the effect of
PGR applications on Scarlet Royal table grapes to determine their incidence on
gray mold and quality parameters during post-harvest storage.
CHAPTER 2: LITERATURE REVIEW
Table Grapes: Importance and Production in the World and the United States
Table grapes are one of the main three fresh fruits consumed in the US
along with bananas and apples. From the total consumed tonnage 53.5% is
grown in California, while the remaining 46.5% corresponds to imported
produce (USDA, 2014a; USDA, 2014b).
The total area planted with table grapes in California for 2013 was 36,912
hectares with 34,047 bearing hectares and 2,865 non-bearing hectares (see
Appendix). There are currently more than 70 different table grape varieties
grown in California, but the majority of the commercialized volume is accounted
only by a dozen of them. These main 12 varieties include Autumn King (1,580
ha); Autumn Royal (1,845 ha); Crimson Seedless (5,021 ha); Flame Seedless (7,394
ha); Perlette (414 ha); Princess (1399 ha); Red Globe (4,456 ha); Ruby Seedless (621
ha); Scarlet Royal (1,831 ha); Sugraone (2,369 ha); Summer Royal (391 ha);
Vintage Red (501 ha) and Thompson Seedless (71,008 ha not considered in the
total acreage for table grapes due to its variety of uses) (CDFA, 2014).
The majority of the table grape acreage in California is located in District
13 and 14 (Table 1). In district 13 the production is concentrated in the counties of
Tulare (10574 ha); Fresno (5020 ha) and Madera (880 ha) while in district 14 the
counties of Kern (16364 ha) and Kings (404 ha) are the primary table grape
producers. The remainder of the total acreage is distributed throughout
California in numerous counties that include Alameda (4 ha); Imperial (72 ha);
Merced (54 ha); San Bernardino (216 ha); San Joaquin (88 ha); San Luis Obispo
(40 ha); Solano (4 ha) and Stanislaus (4 ha) (CDFA, 2013b; CDFA, 2014).
4 4
Table 1: Acreage Standing by County and Year Planted in California for Table
Grapes (CDFA, 2014).
County
2004 &
Earlier
2005
2006
2007
2008
2009
2010
2011
2012
Bearing Non-
Bearing
Total
Alameda 4 0 0 0 0 0 0 0 4 0 4
Amador 0.4 0 0 0 0 0 0 0 0.4 0 0.4
Butte 4 0 0 0 0 0 0 0 4 0 4
Calavera 0.4 0 0 0 0 0 0 0 0.4 0 0.4
Contra Costa 1 0.4 0 0 0 0 0 0 1.4 0 1.4
El Dorado 2 0.4 0 0 0 0 0 0 2.4 0 2.4
Fresno 3681 173 169 213 116 155 373 75 4507 513 5020
Humboldt 0.4 0 0 0 0 0 0 0 0.4 0 0.4
Imperial 72 0 0 0 0 0 0 0 72 0 72
Kern 10452 919 594 788 684 546 1207 662 13984 2381 16364
Kings 218 67 0 17 73 14 0 0 390 14 404
Lake 0 0 0 0 0 0.4 0 0 0.4 0 0.4
Madera 633 28 30 11 36 0 82 61 739 143 882
Mendocino 1 0 0 0 0 0 0 0 1 0 1
Merced 5 0 0 0 0 0 0 0 5 48 54
Monterey 0.4 0 0 0 0 0 0 0 0 0 0.4
Napa 0.4 0 0 0 0 0 0 0 0 0 0.4
Placer 1 0 0 0 0 0 0 0 1 0 1
Riverside 2412 70 80 95 18 52 46 7 2779 19 2797
San Bernardino 215 0 0 0 0 0 0 0 216 0 216
San Diego 0.4 0 0 0 0.4 0 0 0 0.4 0 0.4
San Joaquin 87 0 0 1 0 0 0 0 88 0 88
San Luis Obispo 0 0 40 0 0 0 0 0 40 0 40
Santa Cruz 2 0 0 0 0 0 0 0 2 0 2
Shasta 3 0 0 0.4 0 0 0 0 3.4 0 3.4
Siskiyou 0 0 0 0 0 0 0 0 0 0 0
Solano 1 0 0 0 3 0 0 0 4 0 4
Sonoma 1 0 0 0 0 0 0 0 1 0 1
Stanislaus 3 0 0 1 0 0 0 0 4 0 4
Tehama 3 0 0 0 0 0 0 0 3 0 3
Tulare 6992 482 512 458 619 366 511 305 9430 1145 10574
Yolo 7 1 0 0 0 0 0 0 8 0 8
State Total 24804 1740 1425 1585 1550 1132 2218 1110 32288 4263 36551
5 5
As with every crop, table grape production is influenced by the weather
characteristics of a specific growing region. The research presented in this project
is based on a table grape production site in the Fresno area, thus the climate
characteristics for this county will be described in this chapter.
Fresno County is located in the San Joaquin Valley (SJV) and its climate is
greatly influenced by the surrounding mountain ranges. The Pacific moisture
flow is blocked by the Diablo Range that generates a dry climate in Fresno area.
Summers are characterized by hot temperatures and sunshine while rainfall
events, though infrequent, do occur but generally in small amounts. During the
fall season, temperatures will slightly cool down and precipitation can become
more frequent. By mid-October and November frontal passages become more
common bringing the first widespread rains of the season (Stachelski and Sanger,
2008).
Fresno County Climate
Fresno County is located in the California Climate Zone 13, which has
Fresno city as main reference. The characterization of this region includes data
collected mainly from Fresno, Bakersfield, Visalia and Porterville. It is located at
Latitude of 36.46 N and a Longitude of 119.43 W (Paciffic Energy Center, 2008)
The mean elevation is 99.97 in Fresno with a variation across the SJV between
30.48 and 182.88 meters above sea level (Stachelski and Sanger, 2008).
Fresno County Temperatures
The summers in Fresno are characterized by almost constant sunshine and
high temperatures. The mean daily temperatures during the three months of
summer are 24.5°C for June, 27.27°C for July and 26.55°C for August. Maximum
6 6
temperatures are usually reached it in the month of July with an average of
35.9°C. Temperatures tend to slightly decrease during the fall (Figure 1).
Figure 1: Average Temperature from 1971-2007. Adapted from Annual
Climatology: Fresno, CA (Fresno County, 2014) and The Weather Channel:
Monthly Weather for Fresno (The Weather Channel, 2014). Accessed 02/2014.
During the winter temperatures are usually mild but occasionally
temperatures can drop to or below freezing. The mean daily temperatures during
winter months are 7.33°C for December, 7.78°C for January and 10.77°C for
February. The lowest temperatures are registered generally in December with a
mean of 2.77°C. During spring, the weather transitions from the winter storms
season to the hot and dry summer (Stachelski and Sanger, 2008).
Fresno County Precipitation
Fresno county is subject to a Mediterranean climate which means that the
summers are hot and dry while winters have mild temperatures and relatively
light precipitation (Fresno County, 2014). The normal annual precipitation for
Fresno is 294.05 mm of which 90% is received from November through April
(Figure 2). The remaining 10% is spread throughout the remaining 6 months and
7 7
can be described as early or late rain events. Data collected in the last 30 years
(1977-2007) showed that 20% of the time early rain events may occur in August
while chances increase to 43% in September and 80% in October (Stachelski and
Sanger, 2008). These early season rains often represent a hazard in fruit
production areas by providing humidity which in combination with warm
temperatures provides adequate conditions for disease proliferation (Bettiga and
Gubler, 2013).
Figure 2: Average Precipitation from 1971-2007. Adapted from Annual
Climatology: Fresno, CA (Fresno County, 2014) and The Weather Channel:
Monthly Weather for Fresno (The Weather Channel, 2014). Accessed 02/2014.
Calendar of Weather Events: Southern San Joaquin Valley
The rain hazard on fruit for the southern SJV is present from mid-August
through the beginning of December since this period coincides with the harvest
time of numerous table grape varieties (Figure 3) (Vasquez et al., 2013).
8 8
Figure 3: Calendar of Weather Events for the Southern San Joaquin Valley
(Vasquez et al., 2013).
Scarlet Royal Table Gapes
Origins and Description of Scarlet Royal Table Grapes
Scarlet Royal is red seedless grape cultivar that was developed by Dr.
David Ramming and Ronald Tarailo from the USDA in Parlier, CA. This variety
was evaluated as B1 that resulted from the highly complex cross C33-30 X C51-
63, and was released in 2006.
Scarlet Royal is medium in vigor and has an average production of 27 kg
per vine when trained to quadrilateral system, pruned to 2 bud spurs and grown
on a Y or open gable trellis system. The clusters are conically shaped and are
large in both size and length. The berries are oval shaped, with a medium to
thick skin and a firm, meaty textured flesh. Each berry has 3 to 4 aborted seeds,
which are imperceptible when consumed. Its taste has been described to be sweet
and neutral. This variety has a dark red color when fully ripened and can achieve
full coloring even when grown under full canopy conditions. At harvest, berries
present 22.0% soluble solids and a Titratable acidity (TA) of 0.55 g/100 mL of
juice (Ramming and Tarailo, 2006).
9 9
This variety can be planted on its own roots or grafted on to different
rootstocks depending on site-specific soil pest and/or soil physical and chemical
conditions. Popular rootstocks used for Scarlet Royal include Freedom and 1103-
P. Differences in yield, fruit quality and vine performance for each rootstock are
yet to be determined (Hashim-Buckey and Ramming, 2008) .
Scarlet Royal is a mid-season variety, ripening uniformly from mid to late
August in the California SJV and can be kept in cold storage for 2 months
without compromising berry firmness. The commercialization of Scarlet Royal
covers the market window between Flame Seedless and Crimson seedless
(Ramming and Jones, 2005).
Considering the total grape volume by variety in California in the past
three years, Scarlet Royal occupied 4th place with a total of 8,672,565 tons in 2012
(CTGC, 2013).
Cultural Practices for Scarlet Royal
The main cultural practices for Scarlet Royal include spur pruning to 2
buds during dormant season, shoot thinning and cluster thinning (see Table 2).
Usually, 2 GA3 applications are performed, the first one at bloom and the second
one for sizing. For Scarlet Royal girdling is not recommended and ethephon
applications are not necessary (Andris et al., 1985; Hashim-Buckey and
Ramming, 2008).
Table 2: Cultural Practices for Scarlet Royal Table Grapes. Variety Type of
pruning
Number
of spurs
per vine
Number
of buds
per spur
Shoot
thinning
GA3
Bloom
sprays
GA3 Sizing
spray
Girlding Ethephon
applicati
on
Cluster
thinning
Scarlet
Royal
Spur 30-40 2 Yes 2-2.5
ppm
20
ppm
No No Yes
10 10
Production Problems and Special Considerations for Scarlet Royal
Scarlet Royal can develop bitter flavors or skin astringency if the time of
harvest is delayed or the total soluble solids (TSS) are over 23%. Harvest should
begin when the fruit is sweet, well balanced and soluble solids are equal or over
17%. To ensure a palatable, high quality fruit, harvest should be continued until
the TSS reach 22% (Hashim-Buckey and Ramming, 2008).
Form the information collected, Scarlet Royal shows a high susceptibility
to Botrytis bunch rot both in the vineyard and during cold storage. This problem
is enhanced by the fact that this is a late variety that might be subject to rain,
which increases berry cracking due to high humidity. Furthermore, Scarlet Royal
tends to have tight clusters and a lack of a thick epicuticular wax that contributes
to its susceptibility to bunch rot.
Pre and Post-Harvest Pathological Problems in Table Grapes
Pre- and post-harvest decay on table grapes is one of the causes of
financial loss in numerous counties. During pre-harvest, decay is mainly caused
by fungi infections such as Botrytis, Rhizopus, Aspergillus and Penicillium as well
as bacteria and yeasts. Post-harvest decay on the other hand is mostly caused by
Botrytis cinerea. However, the abovementioned pathogens, as well as Alternaria,
can damage the stored fruit depending on the storage conditions. Three factors
directly influence the onset and evolution of fruit decay during the pre-harvest
period: a) the presence of pathogenic material, b) favorable environmental
conditions and c) host susceptibility (Fourie, 2008).
During storage, the development of decay causing pathogens is reduced,
but not completely inhibited, by the use of low temperatures. If the storage
11 11
temperature is above 0°C or fluctuates with time, many fungi can mature and
cause damage (Fourie, 2008).
Botrytis Bunch Rot in Table Grapes
Botrytis cinerea and other types of Botrytis are major pathogens for a large
number of field and orchard crops as well as stored and transported products,
which includes table grapes. Epidemics caused by Botrytis cinerea can be severe
and economically damaging in conditions conductive to infection (Elmer and
Michailides, 2007).
Botrytis cinerea causes the disease commonly known as gray mold or
bunch rot. It is of great importance in table grapes since it can infect the berries in
the field and then continue to grow inside them during cold storage. The level of
infection in the field determines the degree of susceptibility of the grapes to the
disease before cold storage as well as the variety, the condition of the fruit at
harvest and the effectiveness of control measures (Gubler et al., 2006).
This fungus can grow on any succulent grape tissue such as shoots, young
leaves and flower parts or even on stressed or dead tissue. The most susceptible
cultivars are the heavy canopy cultivars with tight clusters and thin-skinned
berries, especially when growing conditions are humid (Bettiga and Gubler,
2013).
Symptoms of Botrytis Bunch Rot
In the vineyard, Botrytis bunch rot symptoms can be seen on foliage, fruit
and canes. On the leaves, soft brown tissue forms in sections that are followed by
the death of the infected part. Yield can often be reduced by the death of smaller
infected shoots and their inflorescences and older shoots can wilt or break at the
infection site. In the majority of the cases, as a result of water accumulation,
12 12
infections take place on the joints of the leaves and inflorescences axis with the
main shoot (Bettiga and Gubler, 2013; Emmet et al., 2007).
Bunch rot usually starts when blossoms are infected with spores during
rainfall. These spores become dormant after infecting the flowers until veráison,
when the pulp gets infected (Bettiga and Gubler, 2013). This initial stage of
Botrytis bunch rot is known as the “slip-skin” stage. This distinctive characteristic
is a result of the loosening of the overlaying skin of the grape that can be easily
separated from the pulp. After the first stage, a brown discoloration develops
which results in copious production of brown spores (Snowdon, 1990).
Weather conditions like moderate temperatures, high moisture and low
wind speed can favor the cracking of the berries’ epidermis in which mycelium
and spores are generated giving the characteristic gray velvety appearance of the
Botrytis bunch rot. The disease can spread from berry to berry and give the
appearance of a nested infected cluster. Furthermore, the percentage of infected
berries can increase if favorable conditions are maintained and if the fungus
reaches the rachis, the affected berries can raisin (Bettiga and Gubler, 2013).
The shoots, spots of soft brown rot develop on shoot stems. The infected
shoots can break at the nodes where an internal brown discoloration can be seen
(Emmet et al., 2007).
In storage, the appearance of symptoms can be delayed due to low storage
temperatures. The first symptoms are water soaked lesions on the berry skins
which can progress to slip-skin in 1-4 days at 0°C. Following the slip-skin phase,
gray-brown lesions develop on the surface of the grape (this symptom may not
be evident in red or black grapes) and subsequently, mycelium starts growing
out of the berry. Within 1 week, the mycelium can infect adjacent berries and
results in the development of infection nests with a gray-white mycelium. In the
13 13
final stages of decay, the berries become dark and lose their juice. The rachis can
also become infected and turn brown with subsequent mycelium formation. This
mycelium can move through the stems and infect other berries and berries
attached to infected stems can dry out (Bettiga and Gubler, 2013).
Botrytis cinerea Life Cycle
Overwintering: Botrytis can survive the winter either on the surface or
inside colonized tissue as sclerotinia (dormant structure), inside the vine canopy
or on the ground. The main sources of these dormant structures are mummy
clusters form the previous year and same year infected canes. During spring, the
sclerotinia germinate after rain or irrigation events and produce conidia (spores)
that are disseminated mainly by wind (Figure 4) (Bettiga and Gubler, 2013;
Emmet et al., 2007).
Figure 4: Botrytis cinerea life cycle (Marois et al., 1992).
14 14
Germination: With continuous free water and nutrients, spores of Botrytis
cinerea can germinate on the surface of healthy or damaged berries (Bettiga and
Gubler, 2013). The length of the moisture period necessary to produce infection
varies with the ambient temperature (Nelson, 1950), where hot temperatures
accelerate the drying of the fruit which reduces germination. Periods of no
available water of 15 minutes or less are sufficient to halt germination.
Germination and infection takes place at an optimum temperature of 22°C. At
32°C and above, spores cease to grow but they can do it at a slow pace during
storage with temperatures as low as 1°C (Bettiga and Gubler, 2013).
Infection: Under humid conditions the spores can infect flowers, succulent
young stems and leaves in the early spring. Later in the season, the berries
become more prone to infection as the sugar content increases and the skin
softens. The spores can penetrate the grape through wounds or directly through
intact skin. The main protection against Botrytis infections comes from the berry
skin and epicuticular wax, therefore any factor (for example: cultural practices
and chemical applications) that can alter the physical and chemical
characteristics of these, will affect the susceptibility of the berries to infection
(Bettiga and Gubler, 2013). Dead and infected flower parts that remain within the
cluster can become a source of infection (Emmet et al., 2007)
Infected berries show cracks where more spores are developed, and these
spores can rapidly spread to uninfected grapes especially after a rain event late
in the season. If high temperatures and low humidity conditions prevail, infected
berries may dry up but the fungus will remain alive and continue to grow once
favorable conditions are restored (Bettiga and Gubler, 2013).
15 15
In stored grapes the initial infection starts in the vineyard and spreads
within the storage container. At this stage, the spores produced asexually
(conidia) and are not an important source of infection (Snowdon, 1990).
Effect of Cluster Tightness on Botrytis Bunch Rot and Other Infections
Cluster architecture has a dramatic influence on the development of
Botrytis bunch rot epidemics since it directly impacts the berry’s surface
microclimate. The compactness of the cluster determines the length of time that a
cluster retains water and consequently tight clusters take longer to dry than lose
clusters (Vail and Marois, 1991). Having a wet surface provides the needed
conditions of free water and humidity for conidia to germinate and infect the
berries (Carre, 1985).
Tight clusters provide a high ratio of interior to exterior berries which
results in high surface contact area between them (Vail and Marois, 1991). The
direct contact between grapes interferes with the normal development of
epicuticular wax, making the berries more susceptible to Botrytis infections
(Marois et al., 1986). This is important for disease prevention infections since the
epicuticular wax serves as a protective layer against Botrytis infections and other
threats such as dissecation, insect attack, physical abrasion, frost and radiation,
bacterial infections and wind injuries (Martin and Juniper, 1970).
Also, grape varieties that present a tight arrangement of the berries in the
cluster are more susceptible to berry splitting and cracking which allows
colonization of the berry by numerous disease spores consequently causing berry
breakdown (Barbetti, 1980). Generally, the more berries per centimeter a cluster
has, the higher the rot incidence and severity it presents. Compactness may affect
the number of retained floral debris to the time of berry ripening and can
16 16
increase contact between berries and debris facilitating retained debris to have an
important role in rot development (Hed et al., 2009).
Furthermore, cluster compactness can affect the efficacy of fungicide
sprays applied to control diseases. During ripening, when berries are highly
susceptible to bunch rot, the pesticides may not penetrate to the inside surface of
compact bunches which reduces the effectiveness of disease control (Hed et al.,
2009).
Botrytis Bunch Rot Pre- and Post-Harvest Decay Control
Botrytis bunch rot control in the vineyard can best be achieved by
applying an integrated approach that considers the combination of different
practices. The main target of the integrated program is to adequately manage the
fruit zone to reduce humidity and facilitate the drying of bunches after a pre-
harvest rain event. Canopy density and phenological stages of the clusters are
key factors in determining chemical application efficacy. By applying both
cultural and chemical control methods the disease can be properly managed.
Cultural practices: These include canopy management, sanitation practices,
irrigation management, berry damage reduction practices and plant resistance
(Bettiga and Gubler, 2013; Pearson and Goheen, 1998).
Chemical control: During the dormant period lime sulfur is commonly
used as a clean-up product to reduce the overwintering sclerotia. Applications
are usually performed at a rate of 93.61 l/ha in a high volume of water (Bettiga
and Gubler, 2013). During the growing season several fungicides can be used to
control diseases such as Cyprodinil, Fenhexamid, Iprodione, Pyraclostrobin,
Captan, Dichloran and Mancozeb (Table 3) (Gubler et al., 2014). To optimize the
fungicide coverage, adjuvants are generally added to the tank mix. To prevent
17 17
the development of resistance, fungicides with different modes of actions should
be rotated. Spray programs are planned according to the vineyard’s Botrytis
history, cultivar susceptibility and weather conditions that can favor the
development of the disease. Usually vines are sprayed at bloom, cluster pre-
close, veráison and pre-harvest. During bloom spray applications multiple
applications may be necessary depending on the abovementioned conditions.
The best time for fungicide application is when the favorable environmental
conditions for rot development have been forecasted and before rain events
(Bettiga and Gubler, 2013; Emmet et al., 2007; Pearson and Goheen, 1998).
Sanitation: Since the fungus can survive on mummy clusters, it is
recommended that during pruning all clusters are removed from the vines and
incorporated into the soil. By maintaining a clean vineyard with no fruit left on
the vines, the source of inoculum for the following year can be reduced (Bettiga
and Gubler, 2013).
Canopy management: The objective of canopy management is to create a
non-favorable microclimate for fungus development by exposing the clusters to
light and increased wind speed to reduce drying time after wetting. Canopy
management starts with the vineyard design. The selection of rootstocks and
scion, trellis system, pruning method and plant spacing are important since they
will have an effect on canopy density (Pearson and Goheen, 1998). The
orientation of the rows can also influence canopy microclimate and it should be
selected according to the site’s climate conditions. Other practices, which can be
annually manipulated such as irrigation and fertilization, can affect the canopy
density by influencing main and lateral shoot growth. For short-term canopy
manipulation several practices are recommended. Shoot thinning, shoot
positioning, leaf removal and hedging practices reduce canopy density and
18 18
Table 3: Fungicide Efficacy for Botrytis and Summer Bunch Rot Control
(Adaskaveg et al., 2013).
Trade Name Active Ingredient Botrytis Summer Bunch Rot
Abound Azoxystribin + --
Flint Trifloxystrobin ++ ++
Elite/Orius/Tebuzol Tebuconazole ++ ++
Quadris Top Azoxystrobin/difenoconazole ++ ++
Inspire Super Difenoconazole ++++ ++
Luna Experience Fluopyram/tebuconazole ++++ ++
Luna Tranquility Fluopyram/pyrimethanil ++++ ++
Mettle Tetraconazole --- +
Pristine Pyraclostrobin/boscalid ++++ +++
Sovran Kresomix-methyl ++ ++
Topsin-M/T Thiophanate-methyl ++ ++
Copper Copper ++ +++
Elevate Fenhexamid ++++ ++
Ph-D Polixin-D +++ +++
Rovral + Oil Iprodione ++++ ---
Scala Pyrimethanil ++++ ++
Switch Cyprodinil/fludioxonil ++++ ++
Vangard Cyprodinil ++++ ++
Captan Captan +++ +++
Dithan/Manzate/Pen
ncozeb
Mancozeb ++ ---
Rovral/Iprodione/Ne
vado
Iprodione +++ ---
Ziram Ziram + +
Rating: ++++ = Excellent and consistent, +++ = Good and reliable, ++ = Moderate and
variable, + = Minimal and often ineffective and --- = ineffective.
19 19
increase light penetration and air movement. Timing is a key factor in the use of
these practices since the effect is only temporary and canopy regrowth may occur
(Bettiga and Gubler, 2013). Moreover, these practices will vary in different
climate regions. In warm weather production areas leaf removal should not be
excessive since fruit sunburn may occur and if removed later in the season the
damage can be severe. If leaves are removed early in the season at cluster set, the
berries can develop a thick cuticle that helps prevent both sunburn and Botrytis
infection (Gubler et al., 2014).
Irrigation: Selecting the correct type and managing the level and timing of
irrigation can be a tool to help control the disease. The use of overhead sprinklers
should be avoided specially close to harvest to reduce Botrytis levels. Irrigation
timing should be adjusted to the prevalent climate since it is recommended that
clusters should not remain wet for more than 15 hours. Drip and furrow
irrigation should also be utilized thoughtfully because high volumes of water can
result in dense canopies that provide favorable conditions for rot development
(Bettiga and Gubler, 2013).
Berry damage reduction practices: Controlling insects (such as leafroller
caterpillars) and birds that feed on berries reduces the wounds that serve as
entry points for fungal infections. Other diseases such as powdery mildew can
cause berry cracking, therefore controlling this disease also helps prevent Botrytis
bunch rot infections. Furthermore, all injuries related to canopy and cluster
management should be minimized as they all contribute to the development of
the disease (Bettiga and Gubler, 2013; Emmet et al., 2007).
Plant resistance: The combination of numerous factors determines a
variety susceptibility or resistance to Botrytis bunch rot. Generally, white grape
varieties with thin-skinned berries are more susceptible to Botrytis cinerea. On the
20 20
other hand, research has shown that cluster architecture and tightness have a
greater impact on susceptibility rather than the characteristic of individual
berries (Bettiga and Gubler, 2013; Pearson and Goheen, 1998). Research has
shown that some of the characteristics of the more resistant varieties were a thick
epidermis and external hypodermis with numerous cell layers, low number of
pores and a thick cuticle (Gabler et al., 2003).
Post-harvest control begins with correct management of the disease in the
vineyard. Harvest during rainy periods should be avoided especially when
clusters are wet and only be resumed once they are completely dry. During
harvest, the damaged and decayed berries should be trimmed from the clusters.
Trimmed grape clusters should be placed in an adequately chosen box without
over packing it (Gubler et al., 2013).
After harvest, the fruit should be rapidly cooled and handled with care.
Sulfur dioxide (SO2) is generally used for disease control in cold storage. The SO2
gas is an effective fungistat that prevents new infections by killing spores and
inhibiting mold growth on the berries surface although it cannot stop established
infections. Sulfur dioxide can be applied by using fumigation technology or in-
package SO2 generators. These rely on potassium or sodium metabisulphite and
can be found as chemical impregnated sheets, plastic sachets that contain either
the solution or powder formulation (Snowdon, 1990). Traditional fumigation
practices include initially gassing fruit with 5000 ppm SO2, followed by
supplementary fumigations at 7 to 10-day intervals with 2500 to 5000 ppm.
Currently, a more developed system is applied to decrease residue and
environmental pollution while increasing worker safety. This modern system
consists of an initial application combined with forced-air cooling and additional
21 21
fumigations follow at weekly intervals. The applied quantity depends on the
number of boxes in storage and the packaging material (Gubler et al., 2013).
Problems associated with the use of SO2 for post-harvest Botrytis bunch rot
control includes the presence of residues that exceed the 10mg/kg tolerance for
most countries and the impossibility of its use on organically certified grapes.
Furthermore, repeated or high dosage fumigations may produce bleaching
injuries on the surface of the berries which affects the commercializing
potential.(Gabler and Smilanik, 2001). Different control methods are currently
being researched to escape the problems associated with SO2 use. Sub-lethal
levels of ethanol in combination with potassium sorbate proved to be effective in
controlling post-harvest Botrytis disease (Karabulut et al., 2005). With brief
immersions of detached berries in ammonium bicarbonate, sodium bicarbonate
and ethanol, gray mold postharvest infections could be controlled with similar
effectiveness as SO2 fumigations. Furthermore, these treatments have minimal
environmental and worker safety issues and because of their low toxicity they
pose a minimal ingestion hazard (Gabler and Smilanik, 2001).
Blue Mold Rot and Rhizopus Rot in Table Grapes
Blue mold rot: Following Botrytis bunch rot, blue mold rot is considered
the second most damaging disease for stored grapes. It is caused by a number of
Penicillium species such as Penicillium canescens Sopp and Penicillium citrimun
Thom (India), Penicillium cyclopium Westling (Israel) and Penicillium expansum
(USA, Chile and Germany). Along with other fungi (Aspergillus spp, Alternaria
tenuis, Cladosporuim spp and Rhizopus arrizhus) Penicillium species are usually
involved in summer bunch rot complexes (Bettiga and Gubler, 2013).
22 22
The symptoms for blue mold include abundant presence of white mold
that subsequently produces green-blue powdery spores on stems and berries.
The infected grapes become watery and soft and release a distinctive moldy odor
(Snowdon, 1990).
Penicillium spp. life cycle: Conidia from Penicillium species survive on
decaying plant material and can be dispersed by wind, water and insects. Injured
berries are predisposed to infection throughout the season and mold can even
spread through the bunches during refrigerated storage (Snowdon, 1990).
Rhizopus rot: This disease is caused by different species of Rhizopus, such
as Rhizopus oryzae Went & Prinsen Geerligs, Rhizopus stolonifer Lind and Rhizopus
arrizhus. Rhizopus rot can be recognized by the presence of spherical spore-heads
that will change from white to black, covering the surface of berries in the cluster
(Snowdon, 1990). This fungus can also be found in summer bunch rot complexes.
The presence of this pathogen in stored grapes indicates that storage conditions
were mismanaged since the fungus growth is inhibited at temperatures below
4°C (Bettiga and Gubler, 2013).
Rhizopus spp life cycle: The Rhizopus spores (sporangiospores) are present
in the soil and on plant debris and disseminated by wind. The berries are subject
to infection during the entire grape growing season. Injured berries are the entry
points for primary infections but Rhizopus oryzae can also penetrate healthy berry
skins when exuded grape juice is present. Once the disease is established,
adjacent sound berries can be rapidly infected especially in high temperature
conditions (Snowdon, 1990).
23 23
Aspergillus Rot and Cladosporium Rot in Table Grapes
Aspergillus rot: This fungus commonly prevails in production areas with
prolonged hot temperatures and is also often associated with bunch-rot
complexes. The presence of this fungus in harvested fruit can be a result of
prolonged high temperatures in storage thus, in normal storage conditions
Aspergillus rot is not usually a problem (Nelson, 1979).
This disease is caused by two Aspergillus species named Aspergillus niger
and Aspergillus carbonarius. These are usually the first fungus species to colonize
wounded berries in the SJV and are generally an important contributor to
summer bunch rot complexes (Bettiga and Gubler, 2013). The spores can easily
be seen and are usually black and but in some cases another form with brown
spores can infect the berries. The fungus destroys the berry pulp, creating a pale
and watery spot below the mycelium while releasing a sour odor (Snowdon,
1990).
Aspergillus niger life cycle: The fungus survives on plant debris in the soil
and its development is favored by warm temperatures between 25°C and 35°C.
Air currents disseminate the conidia which infect the berries through surface
wounds (Snowdon, 1990). Aspergillus only infects the berries after the
phonological stage of veráison. Once the fungus invades the tissue, the pulp goes
through rapid decay which enables colonization of other fungi and yeasts as well
as insect visitation (Bettiga and Gubler, 2013). High temperature conditions
accelerate the spreading of the fungus through the cluster. The infections can
continue through post-harvest storage (Snowdon, 1990).
Cladosporium rot: This fungus is commonly found in stored grapes due to
its ability to grow at very low temperatures (0°C). It is caused by Cladosporium
herbarum and the symptoms include circular black spots under the skin that
24 24
subsequently forms velvety olive-green mold (Snowdon, 1990). Cladosporium
cladosporioides can also be a problem in stored grapes and both species are usually
found in summer bunch rot complexes. If the berries are subject to sunburn in
the vineyard, this fungus can colonize the injured tissue. During cold storage the
affected tissue begins to break down and brown spots appear on the surface of
the berry. When these berries are removed from storage, a green sporulation is
produced on the rotten tissue (Bettiga and Gubler, 2013).
Cladosporium spp. life cycle: This fungus survives on dead plant material in
the soil. Spores (conidia) are disseminated in the air and usually infect berries
through open wounds that were caused by rain or rough handling. The fungus is
also capable of direct penetration through the intact skin. Primary infection
occurs before harvest and high incidence of disease is frequently associated with
wet conditions (Snowdon, 1990).
Summer Bunch Rot Complex Pre- and Post-Harvest Control
The most suitable control for summer bunch rot complex (Aspergillus spp,
Penicillium spp, Cladosporium spp and Rhizopus spp) is minimizing berry injuries
before, during and after harvest. Controlling damage caused by canopy and
cluster management, insects, birds and early-season powdery mildew infections
can significantly reduce the incidence of bunch rot complex in the vineyard.
Berry cracking can be prevented by thinning the grape clusters that will reduce
tightness and overcrowding of berries. There are numerous approved fungicides
currently available and used (Table 3, p. 18) to control summer bunch rot
problems (Adaskaveg et al., 2013). Nonetheless, chemical treatments have
proved to be somewhat ineffective since most of them only target one or two
pathogens rather than the entire bunch rot complex (Muthuswamy et al., 1971).
25 25
During cold storage the fruit must be handled with care to avoid injury
and SO2 applications should be performed to kill existing spores on the berry
surface. The fruit must be stored at an adequate and constant low temperature
(Snowdon, 1990).
Plant Growth Regulators: Gibberellins and Cytokinins
Plant growth regulators are a set of organic substances that occur
naturally and have a direct impact on the physiological processes of the plant at
low concentrations. Cell growth, differentiation and development are directly
influenced by hormones but other processes can also be affected by hormonal
activity like stomatal movement (Davies, 2004).
Gibberellins
Gibberellins or GAs are a group of substances based on the ent-
gibberellane structure and include more than 125 members in this group of
hormones. The main gibberellin in plants is GA1, but the most abundant one is a
fungal product, GA3. This hormone regulates many stages of the higher plant’s
development. The effects of gibberellins include stem growth (GA1 stimulates
cell division and elongation), bolting in long day plants, induction of seed
germination, enzyme production during germination, fruit setting and growth
(in grapes, exogenous applications can induce fruit set and growth) and
induction of maleness in dioecious flowers (Davies, 2004).
Effects of Gibberellic Acid (GA3) on Grapes
Gibberellic acid is a metabolic product derived from the fungus Gibberella
fujikuroi first found in rice in Japan. This hormone can be obtained by fermenting
large quantities of the Gibberella fujikuroi (Brian, 1959).
26 26
Gibberellic acid has been used in table grape production for many years
with a wide variety of applications and purposes. Application timing and
concentrations have different effects on different grape varieties.
Pre-bloom applications: Can have numerous effects such as seedlessness,
flowering acceleration, extension or shortening of flowering period, increasing or
decreasing berry size, high or low presence of shot berries. The course of these
effects is highly dependent on application timing, concentration and grape
variety. The varieties ‘Delaware’ and ‘Early Campbell’ showed optimum
outcomes if applications are conducted between 23 and 10 days before full
bloom. This means that full bloom can be accelerated, flowering period can be
extended and seedlessness can be achieved with proper application timing.
Other varieties like Vitis labrusca Baile, Kyoho, Muscat Bayley A have responded
to GA3 application by reduction seedlessness. This effect may be a result of the
sensitivity of the ovules to gibberellins that induces parthenocarpic berry
development or by inhibition of pollen germination and pollen tube growth.
(Fukunaga and Kurooka, 1987; Jeong et al., 1998; Kimura et al., 1996; Motomura
and Ito, 1972).
Bloom applications: Often used when fruit set is excessive and results in
very tight clusters when other practices such as trunk girdling are not enough to
solve the problem. As in pre-bloom applications, the effect that bloom
applications may have is also dependent on timing, concentration and variety.
Nevertheless, some generalizations can be made on the effects of GA3 sprays
during bloom regarding fruit set, berry size and fruit ripening. Applications at
25-75% capfall in Thomson Seedless usually results in loose clusters and enlarged
berries where later applications may not have the same effect since it is believed
that the apical berry tissue decreases its response to GA3. These late bloom
27 27
treatments also favor berry elongation but have little effect on berry width which
tends to stay constant regardless of application time (Christodoulou et al., 1968).
Other varieties may have later optimum application time such as Crimson
Seedless. A single spray between 80-100% bloom significantly reduces berry set,
increases berry size and length without reducing cluster weight or cluster
number per vine. This single treatment is enough to cause cluster thinning and
reduce the compactness but if successive applications follow, thinning can be
excessive and a high number of shot berries may appear (Dokoozlian and
Peacock, 2001). Data supports that the increase in berry weight is a result of the
hormone induction to movement of assimilates into the berries shortly after
application (Weaver et al., 1968).
Repeated bloom applications can also have an effect on fruit maturation
on Thomson Seedless. Growers, as a common practice, spray the clusters with
GA3 up to eight times between bloom and fruit set to increase berry size. It has
been demonstrated that the effect on size decreases after the fourth application,
but maturation can be significantly affected. Repeated sprays can result in
reduced TSS and high acidity level which signifies a delay in ripening (Ben-Tal,
1990). The concentration at which GA3 is used can vary depending on the desired
results. Low concentrations (2.5 to 5 ppm) can be sufficient to cause cluster
loosening without significantly increasing berry size. On the other hand,
concentrations from 5 to 40 ppm increase berry weight and elongation. These
different concentrations tend to change berry size by affecting its length while
keeping berry diameter constant (Christodoulou et al., 1968; Weaver et al., 1968).
GA3 levels between 20-50 ppm can affect sugar concentration by
increasing fructose and glucose quantities at harvest in varieties like Cardinal,
Michele Palieri and Black Corinth (Rusjan, 2010; Weaver et al., 1968). Conversely,
28 28
organic acid and amino acid concentrations usually decrease with high GA3
levels (Weaver et al., 1968). High dosages or over application of GA3 can have
negative effects during post-harvest storage, increasing hairline cracking
incidences and shatter after 30 to 60 days in cold storage at 0°C (Rusjan, 2010;
Zoffoli et al., 2009).
Fruit-set applications: Used for berry sizing usually after one bloom
application of 15 ppm. In some varieties such as Thompson Seedless, fruit-set
sprays can be repeated up to three times to increase berry length (Singh et al.,
1978). In Thompson Seedless, Ruby Seedless and Black Corinth fresh and dry
berry weights increase with GA3 applications (Harrell and Williams, 1987;
Weaver et al., 1968). At this stage, clusters become a stronger sink for assimilates
and therefore the berries have a stronger response to the hormone application by
significantly increasing size and weight (Weaver et al., 1968). Gibberellic acid
induces cell enlargement, which increases berry size but decreases cell density so
treated berries present a thinner skin than untreated berries. This reduction in
cell density and thinned berry skin can increase susceptibility to decay during
post-harvest storage (Ben-Arie et al., 1998).
High GA3 concentrations at this stage can negatively affect berry
adherence which results in an increase of berry shatter after 25-30 days in cold
storage. Moreover, although pedicel diameter increases, its flexibility along with
the rachis flexibility is reduced with increasing GA3 concentrations (Retamales
and Cooper, 1993; Singh et al., 1978). The increase in pedicle rigidity restricts the
accommodation of the berries during harvest and post-harvest manipulation
which results in high percentages of berry detachment (Retamales and Cooper,
1993).
29 29
Veráison applications: GA3 sprays can have an effect on berry texture,
increasing both flesh and skin firmness (Singh et al., 1978).
Pre-harvest applications: Late applications of GA3, especially at high
dosages, can result in delayed fruit ripening and increased berry blemishes for
Sultanina and Waltham Cross grapes (Wolf and Loubser, 1992).
Cytokinins
Cytokinins or CKs are derived from adenine. The most common CK in
plants is Zeatine and its biosynthesis takes place in roots and seeds. The effects of
this hormone include cell division, growth and development. Exogenous
applications induce cell division when auxin is present and it is endogenously
found in gall tumors. It also promotes morphogenesis as it initiates shoot
elongation. Furthermore, CK play a role in lateral bud growth, leaf expansion,
chloroplast development (which increases chlorophyll accumulation) and it
delays leaf senescence (Davies, 2004). CPPU is a synthetic CK also known as
Forchlorfenuron [N-(2-chloro-4pyridyl)-N’-phenylurea] commonly used as a
plant growth regulator in numerous crops (Pubchem, 2014).
Effects of Cytokinin (CPPU) on Grapes
The effects of CPPU applications on table grapes are numerous and the
response level is related to the stage of berry development at the time of
treatment. Mostly, at low concentrations, this hormone promotes berry set and
development (Nickell, 1985). Furthermore, synthetic CK can cause different
reactions depending on the cultivar and amount applied (Strydom, 2013).
Pre-bloom and bloom applications: berry set percentage increases when
CPPU is applied at pre-bloom or bloom. Conversely, berry size is hardly affected
30 30
with pre-bloom applications and slightly affected with bloom applications
(Nickell, 1986a).
Fruit-set applications: The application of CPPU at this stage has different
effects on the berries and the magnitude of these effects is highly concentration
dependent with the best results obtained between 5 ppm and 15 ppm. In
numerous varieties such as Flame Seedless, Red Globe, Crimson Seedless,
Thompson Seedless, Sultanina, Sovereign Coronation, Simone and Summerland
selections low CPPU concentrations increase berry size and fruit set (Navarro et
al., 2001; Retamales et al., 1995; Reynolds et al., 1992; Strydom, 2013). Treated
berries of Thompson seedless and Kyoho were heavier and rounder since length
is reduced due to a proportionate increase in berry diameter. (Dokoozlian et al.,
1994; Han and Lee, 2004). Also, Flame Seedless, Himrod and Perlette treated
berries are generally firmer than non-treated berries and the firmness increases in
a linear fashion with increasing CPPU concentrations (Ben-Arie et al., 1998; Peppi
and Fidelibus, 2008; Zabadal and Bukovac, 2006). This change in firmness may be
a result of skin thickening due to increased cell division (and cell density) caused
by CPPU applications. Furthermore, susceptibility to disease was reduced in
treated berries due to the thickened skin, that provides mechanical resistance to
pathogen invasion and therefore storage potential is increased (Ben-Arie et al.,
1998).
For all the tested varieties the general appearance of the clusters was also
affected. Cluster length, diameter and weight increased (Han and Lee, 2004) as
well compactness (Zabadal and Bukovac, 2006). In Sultanina, Perlette and
Superior table grapes the rachis and pedicels thicken and increase in weight,
which strengthens the attachment of the berry and reduces post-harvest shatter
(Ben-Arie et al., 1998; Navarro et al., 2001; Retamales et al., 1995).
31 31
Treatments with CPPU can also delay berry maturity, which is to be
expected since cytokinin-like compounds are known to slow senescence. At
harvest, this effect results in reduced TSS, and pH while TA is increased. This
may become a viticultural concern for late-season varieties, or those where an
early market is critical (Navarro et al., 2001; Peppi and Fidelibus, 2008; Reynolds
et al., 1992). The reduction in TSS is inversely related to the CPPU concentration,
and it can be reduced by 4-10% (Zabadal and Bukovac, 2006).
Moreover, both skin anthocyanin concentration and color were found to
significantly decrease in Flame Seedless; Sultanina; Kyoho and Sovereign
Coronation grapes with CPPU applications (Han and Lee, 2004; Navarro et al.,
2001; Reynolds et al., 1992). Flame seedless berries become uniformly light
colored with less red and more green which translates into increased Lightness
(L*) and Hue (hº) values (Peppi and Fidelibus, 2008).
Many varieties show improved post storage quality with CPPU
applications since rachis necrosis and berry abscission are significantly reduced
after 30 days in cold storage at 1°C (Dokoozlian et al., 2000; Zabadal and
Bukovac, 2006).
Pre-veráison and veráison applications: When CPPU is applied past 9 mm
of berry diameter in Himond table grapes, the response for berry size and mass
are similar than at fruit set and only the magnitude of the response decreases as
berry diameter increases (Zabadal and Bukovac, 2006). In Red Globe grapes,
parameters such as TSS, TA and pH are not affected by CPPU applications at this
stage but berry firmness can be increased with concentrations from 6-9 ppm
(Avenant and Avenant, 2006).
32 32
Effects of the Combination of GA3 and CPPU on Grapes
The combination effects of plant growth regulators on table grapes has not
been extensively studied and the results vary greatly depending on numerous
factors like grape variety, GA3 concentration, number of GA3 applications, CPPU
concentration and time of application.
In varieties such as Flame Seedless, Red Globe, Crimson Seedless and
Sultanina the combination of GA3 and CPPU results in larger berries and heavier
clusters than non-treated clusters (Strydom, 2013).
Other berry parameters are affected differently depend mostly on the
grape variety and CPPU concentration applied. When GA3 and CPPU are
combined, berry firmness in Flame Seedless is reduced (Strydom, 2013) while
firmness increase in Red Globe (Avenant and Avenant, 2006). In Thompson
Seedless there is no apparent effect (Ben-Arie et al., 1998). Red Globe, Flame
seedless and Crimson Seedless sugar accumulation and maturity is delayed. The
effect on TA differs greatly depending on the variety, while in Red Globe TA
levels decrease in Flame Seedless. Titratable acidity is increased with the
combination of both hormones (Avenant and Avenant, 2006; Strydom, 2013).
Berry quality in cold storage is influenced by the management of plant
growth regulators during the grapevine growing season (Zoffoli et al., 2009).
Pedicel thickness increases in clusters treated with both GA3 and CCPU in
varieties such as Thompson Seedless, Red Globe, Ruby Seedless and Sultanina
(Navarro et al., 2001; Zoffoli et al., 2009) which can result in high percentages of
loose berries (shatter) (Strydom, 2013; Zoffoli et al., 2009). Furthermore, cell
density and skin thickness of berries treated with both plant growth regulators
are equal to those only treated with GA3 which can affect susceptibility to disease
infection (Ben-Arie et al., 1998). Thompson Seedless and Ruby Seedless develop
33 33
hairline cracks during storage when treated with GA3 and CPPU and can present
a high incidence of gray mold (Zoffoli et al., 2009).
In general, all the CPPU effects are depressed with GA3 (Ben-Arie et al.,
1998) and all GA3 effects are reduced with the addition of CPPU but general
tendencies remain (Navarro et al., 2001).
Cluster and Berry Thinning
Effects of Cluster and Berry Thinning on Grapes
Cluster architecture has an effect on disease incidence. Wine grape
varieties such as Carignane, Chenin Blanc, Zinfandel, Barbera; Semillon and
French Colombard present tightly arranged clusters, and are more affected by
Botrytis bunch rot than those varieties with loosely arranged clusters like Muscat
of Alexandria and Cabernet Sauvignon (Vail and Marois, 1991). Even different
clones of the same variety like Chardonnay wine grapes can present differences
in susceptibility to bunch rot depending on the tightness of the clusters (Vail et
al., 1998).
Cluster thinning consists of eliminating whole clusters after bloom once
the berries have set while berry thinning consists on removing only certain
portions of the cluster by eliminating branches of the cluster and the tip of the
rachis (Winkler, 1931).
The process of removing clusters has numerous effects on the remaining
fruit. By eliminating small and misshapen and overly large clusters, the vine’s
energy is utilized by the remaining clusters that will present higher marketable
quality (Winkler, 1931).
34 34
Cluster thinning can be performed at various stages of the vines
reproductive cycle, from pre-bloom through pre-harvest. Pre-bloom thinning
entails removing the inflorescences at an early stage by pinching. If the number
of leaves is kept constant then the retained clusters will benefit from a higher
nutrient supply and consequently present better fruit set and a high percentage
of well-developed berries. Also, the cost of thinning can be reduced if performed
at this stage. However, since cluster shape and berry set are unknown at this
stage, pre-bloom thinning can be risky.
Post-berry set is the optimal and most common time to perform bunch
thinning since cluster shape and number of berries per cluster is easily
determined. Total yield can be decreased when clusters are removed but the
packable yield increases because the remaining fruit generally presents high
quality attributes. The remaining clusters have an increased berry weight and
uniformity along with increased TSS concentration and color development
(Dokoozlian and Hirschfelt, 1995; Winkler, 1931).
Cluster thinning after berry softening reduces berry growth and packable
yield in early and mid-season ripening grapes (Dokoozlian and Hirschfelt, 1995).
Berry thinning is normally used in varieties with compact clusters. It
improves fruit quality by increasing berry weight and improving skin color.
Berry thinning can be performed several times but the best results are achieved
as soon as normal berry drop occurs after bloom. Generally, the earlier thinning
is performed, the greater the berry weight gain will be. Thinning can also
advance berry maturity and can result in more uniform and earlier development
of color (Winkler, 1931). In Red Globe table grapes berry thinning affects organic
acids by increasing malic and tartaric acid concentrations. In this variety TSS and
TA are higher in hand thinned clusters than non-hand thinned ones (Keskin et
35 35
al., 2013). In Rhine Riesling wine grapes, non-thinned clusters present a higher
percentage of infected berries than thinned clusters and usually there is a
positive correlation between cluster weight and the number of rotted berries. The
majority of infected berries frequently have either concentric splitting or cracking
while healthy berries hardly show any open wounds. This shows that by
thinning berries from tightly arranged clusters can reduce berry damage and
subsequently minimize bunch rot incidence (Barbetti, 1980).
Finally, reduction of cluster compactness by berry thinning can increase
spray penetration and efficacy of chemical control programs by allowing the
surface of inside berries to be exposed to the fungicides (Hed et al., 2009).
CHAPTER 3: MATERIALS AND METHODS
Site Selection
The research project was conducted in a commercial Scarlet Royal table
grape vineyard managed by Scattaglia Growers and Shippers, LLC (SGS),
located in Kingsburg, California. All cultural practices performed for the
commercial blocks were executed in the research plot except for no application of
GA3 for sizing.
The total surface area utilized for the study was of 0.556 ha that comprised
of four rows with 208 vines each. The plant spacing was 3.65 m x 1.82 m. The
vineyard was established in 2007 and all vines are own-rooted, meaning no
rootstocks were used for grafting.
Experimental Design
The three different treatments were arranged in a Complete Randomized
Design (CRD). Each treatment was replicated six times and three vines per
replicate were used. One vine between each set of three vines was left as a buffer.
The two adjacent rows to the experimental vines were left untreated to
create a buffer zone from regular PGR applications. The first four vines at both
ends of the rows were excluded in the design as to maintain uniformity of the
conditions of the treated vines.
Treatment Applications
The different treatments (Table 4) were applied on 30 May 2013 and 29
May 2014 at fruit set (E-L Stage 31). Application sprays were performed with
11.35 L hand sprayers and directed to the fruiting zone. Experimental solutions
37 37
were prepared in a 400 L tank with Tripleline Foam-Away and Latron*B 1956
Spreader-Sticker as application adjuvants.
All clusters were manually thinned pre-veráison (E-L Stage 33-35). Third
shoulders and small individual berries from tightly set clusters were removed as
well as weak and poorly positioned clusters.
Post-Harvest Decay Forecasting
Prior to harvest a sample of 100 berries per treatment was taken for decay
forecasting as a method to estimate the type and amount of decay that would
develop on the fruit during storage. An adaptation of the protocol for
Forecasting Decay in Table Grapes for Storage was used (Usda, 1984). For each
treatment the total number of collected berries was divided into two groups and
placed in individual plastic boxes on a mesh rack with a moisturized paper towel
placed underneath. The boxes were left uncovered over night at the pre-cooler
facilities at SGS, LLC for SO2 surface sterilization of the berries. After SO2
fumigation under sterile conditions, berries were rearranged in the box to avoid
direct contact between the berries. Paper towels were re-moisturized with
deionized water and the boxes were kept for three weeks at 15°C for rot
induction. Berry decay was quantified by counting the number of infected berries
Table 4: Treatments, Concentration Rates and Commercial Product
Treatment Concentration Rate Commercial Product
Control No PGR -------
GA3 5 ppm GibGro® 4LS. (4% GA)
GA3+CPPU 5 ppm GA + 6 ppm CPPU GibGro® 4LS (4% GA) +
KimzallTM (0.8% CPPU)
38 38
and calculating the percentage of each type of disease using the total number of
berries per box. The observation of natural incidence of diseases provided
information as to what type of mold could potentially affect the grapes during
storage.
Treatment Harvest
All the treatment plots were handpicked during commercial harvest on 18
September 2013 and 29 August 2014. Each treatment replication was placed in an
individual 9 kg cardboard box and clusters were packed in breathable plastic
bags. After harvest, the fruit was stored at the SGS, LLC commercial cold storage
facility for four weeks at a temperature of 0°C. The boxes were moved to the
Viticulture and Enology Research Center at California State University, Fresno
and kept in cold storage for one week at 7.5°C to simulate the conditions of the
commercial shelf life for table grapes. To prevent further fruit decay each box
contained an individual UVASYS slow release SO2 pad.
Parameters Measured and Instruments Used
Post-Harvest Decay Assessment
For every individual box the total weight of the berries was recorded in
grams. Subsequently, every berry in the box was inspected and those presenting
any abnormalities were placed into a corresponding group. There were a total of
five groups:
1 = Botrytis cinerea infected berries;
2 = Shattered berries;
3 = Cracked berries (longitudinal or neck cracks);
4 = Berries infected by disease other than Botrytis cinerea;
5 = Physically damaged berries or insect damaged berries.
39 39
Botrytis infected berries were identified by the presence of gray/brown
velvety mycelia, faded or pale berry skin color and skins that easily slipped off
while leaving the pulp intact (Bettiga and Gubler, 2013)
Shattered berries were those that easily detached from the rachis when the
cluster was gently shaken and berries that remained loose in the box after all
clusters were examined (Singh et al., 1978)
Cracked berries presented small skin fractures, either around the neck
circling the pedicel or running along the berry length.
Berries with other damage presented insect or bird injuries as well as
trimming shear damage.
Berries with diseases other than Botrytis were affected by numerous molds
such as Aspergillus, Cladosporium, Rhizopus or Penicillium.
After the inspection and classification of the fruit, each receptacle
containing the abnormal berries was weighed and the incidence of each group
was calculated as a percentage of the total weight of the box.
Post-Harvest Berry Quality Assessment
Two sub-samples of 50 unblemished berries were collected from each box
to obtain further quality parameters. The first 50 berries were used to record
berry length, berry width (diameter), berry firmness and berry skin color. Berry
length (mm) was obtained with a hand held digital caliper (General® Ultratech,
USA). Firmness (g/mm) was determined by the amount of force required in
grams to cause a one mm deflection in the berry (FirmTech2, BioWorks,
Wamego, KS). Berry width (mm) was also recorded with the FirmTech2
equipment. Skin color was recorded with a handheld spectrophotometer (Konica
Minolta CM-700d, Japan). The CIELab L*a*b* color space was used where L*
40 40
specifies lightness (values go from 0 for black to 100 for white), a* specifies
chroma (low values indicate green color while high values indicate red color)
and b* specifies hue (low values indicate blue color while high values indicate
yellow color).
The second set of 50 berries was macerated and filtered through a strainer.
From the collected juice TA, pH and TSS was recorded. Titratable acidity (g/L)
and pH were measured with an automatic titrator (Metler Toledo DL15 Titrator,
Switzerland) while TSS (°Brix) was measured with an automatic refractometer
(ATAGO model PAL-1, Japan).
Statistical Analysis
Statistical Package for the Social Sciences (SPSS)TM 10.0 Software was used
to perform multiple comparisons using Analysis of Variance (ANOVA). For
those variables that showed significant differences at a 0.05 level of significance
between treatments, a post-hoc test was performed using Tukey’s Honest
Significant Difference Test (HSD) for treatment mean separation. Year and
replication were considered as random effects and the treatments as fixed effects.
CHAPTER 4: RESULTS AND DISCUSSION
Post-Harvest Decay Forecasting
The rot development trials for the different treatments in 2013 and 2014
provided a guide of the mold types that could potentially develop during cold
storage (Figure 5). The results showed that for both years the grapes were
affected predominantly by four different mold species: Botrytis cinerea, Aspergillus
spp., Cladosporium spp. and Penicillium spp (Figure 6).
In 2013, the control treatment showed 9% of the berries were affected by
Botrytis while other types of mold affected 39%. The GA3 and the GA3+CPPU
treatments were affected by 2% and 6% Botrytis respectively and by other types
of mold 19% and 39% respectively (Table 5).
In 2014, the percentage of Botrytis affected grapes for the control, GA and
GA3+CPPU treatments were 11%, 23% and 23% respectively. The total percentage
of berries affected by other types of mold was 22% for the control, 16% for the
GA3 treatment and 11% for the GA3+CPPU treatment (Table 5).
Table 5: Percentage of Botrytis cinerea and Other Diseases Affecting Control, GA3
Treatment and GA3+CPPU Treatment in 2013 and 2014.
Treatment 2013 2014
Botrytis cinerea (%) Other Disease (%) Botrytis Cinerea (%) Other Disease (%)
Control 9 39 11 22
GA3 2 19 23 16
GA3+CPPU 6 39 23 11
Statistical analysis was not performed for the trial, as the objective was only to
determine the type of mold that could potentially develop during post-harvest cold
storage.
42 42
Figure 5: Grapes Arranged for Post-Harvest Decay Forecasting Showing Infected
Berries.
Figure 6: From Left to Right: Botrytis Infected Berry, Penicillium Infected Berry,
Cladosporium Infected Berry and Aspergillus Infected Berry.
43 43
Experimental Results
Post-Harvest Decay Assessment
The percentage of Botrytis cinerea incidence after 4 weeks of cold storage at
0°C and 1 week at 7.5°C on Scarlet Royal showed no significant differences for
any of the three applied treatments (P = 0.866) (Table7).
However, the percentage of shattered berries after post-harvest storage
was significantly affected by the application of GA3 (P = 0.000, see Table 7). The
data showed that the application of GA3 at a rate of 5 ppm at fruit set resulted in
the highest percentage of shatter at 2.0348% compared to the control treatment
and the GA3+CPPU treatment that showed 0.6494% and 0.3701% shatter
respectively.
The application of GA3 and the combination of GA3+CPPU had no
significant effect after post-harvest storage on the remaining variables,
percentage of cracked berries (P = 0.842), percentage of other damage (P = 0.374)
and percentage of other disease (P = 0.969, see Table 6).
Table 6: Effect of GA3 and GA3+CPPU on Percentage of Botrytis cinerea Incidence,
Berry Shatter, Berry Crack, Other Damage and Other Disease Incidence at Post-
Harvest on Scarlet Royal Table Grapes Treatment Botrytis
cinerea (%)
Berry Shatter
(%)
Berry
Crack (%)
Other Damage
(%)
Other Disease
(%)
Control 1.5292 a 0.6494 a 1.8305 a 3.4252 a 4.0815 a
GA3 2.0579 a 2.0348 b 1.5059 a 5.0025 a 4.1693 a
GA3+CPPU 1.7713 a 0.3701 a 2.0822 a 5.1977 a 3.6950 a
P 0.866 0.000 0.842 0.374 0.969
Mean values within a column followed by the same letter are not significantly
different according to Tukey’s HSD test (P ≤ 0.05).
44 44
Post-Harvest Berry Quality Assessment
The application of GA3 and the combination of GA3+CPPU at fruit set had
no significant effect on normal berry quality parameters after post-harvest cold
storage (Table 7).
Berry length was not affected by the application of either GA3 or
GA3+CPPU when compared to the control treatment (P = 0.203, see Table 7).
Furthermore, the differences in berry width and in berry firmness were small
and not significant (P = 0.289 and P = 0.883, see Table 7). Berry skin color was also
not affected regarding any of the three CIELab parameters Lightness, chroma
and Hue (P = 0.988, P = 0.782 and P = 0.996 see Table 7).
Table 7: Effect of GA3 and GA3+CPPU on Berry Length, Berry Width, Berry
Firmness and Berry Color (Lightness, Chroma and Hue) at Post-Harvest on
Scarlet Royal Table Grapes.
Mean values within a column followed by the same letter are not significantly different
according to Tukey’s HSD test (P ≤ 0.05).
Post-Harvest Juice Quality Assessment
As shown in Table 8, there were no differences between GA3 and
GA3+CPPU applications for the juice quality parameters measured after storage
(Table 8). The pH (P = 0.543), TA (P = 0.918) and TSS were not significantly
affected by the application of either plant growth regulator (P = 0.945).
Treatment Berry Length
(mm)
Berry Width
(mm)
Berry Firmness
(g/mm)
Lightness (L*) Chroma
(a*)
Hue (b*)
Control 27.9142 a 20.8813 a 290.3766 a 45.4816 a 4.5317 a 6.2290 a
GA3 28.4288 a 22.2118 a 287.4603 a 45.3333 a 4.4494 a 6.2067 a
GA3+CPPU 28.9319 a 23.5598 a 283.4788 a 45.5447 a 4.3037 a 6.1295 a
P 0.203 0.289 0.883 0.988 0.782 0.996
45 45
Table 8: Effect of GA3 and GA3+CPPU on Berry Juice pH, Titratable Acidity and
Total Soluble Solids at Post-Harvest on Scarlet Royal Table Grapes.
Treatment pH TA (g/L) TSS%
Control 4.0020 a 7.5922 a 21.4500 a
GA3 4.0110 a 7.4044 a 21.7500 a
GA3+CPPU 4.0720 a 7.4769 a 21.7900 a
P 0.543 0.918 0.945
Mean values within a column followed by the same letter are not significantly different
according to Tukey’s HSD test (P ≤ 0.05).
Discussion
Table grape varieties with tightly arranged clusters, such as Scarlet Royal,
have a high susceptibility to disease infection. These clusters retain humidity for
long periods of time and they are more prone to berry splitting and cracking.
Moreover, the high surface contact area between berries disrupts the
development of the epicuticular wax, which serves as protection. All these
conditions provide favorable conditions for mold spores to germinate and infect
the berries (Barbetti, 1980; Carre, 1985; Marois et al., 1986; Martin and Juniper,
1970; Vail and Marois, 1991). Furthermore, fungicide efficacy for disease control
can be reduced in compact clusters (Hed et al., 2009).
Germination conditions for Botrytis cinerea include temperatures around
22°C and continuous free water on the berry surface. High temperatures, usually
above 35°C, can slow growth and readily dry clusters which reduces overall
spore germination (Gubler et al., 2013; Nelson, 1950). In this experiment, the lack
of differences between treatments and the low percentages of Botrytis infection
shown in the rot development trials can be a result of unfavorable conditions for
spore germination. With temperatures over 35.5°C experienced during the
ripening period in 2013 and 2014 and the lack of rain to provide free water may
46 46
have reduced overall spore germination in the field which consequently reduced
mold growth during cold storage (Gubler et al., 2006). Moreover, due to USDA
spacing problems and government shut down during September of 2013, the
information from the rot development trials was not sufficient to determine
Botrytis incidence for the different treatments and was only used as a guide for
type of mold present.
The application of 5 ppm of GA3 at fruit set resulted in higher berry
shatter than the control or the combination of GA3+CPPU. The use of GA3 has
been proven to cause poor berry adherence by decreasing pedicel flexibility that
restricts the movement of berries and therefore they can easily detach (Retamales
and Cooper, 1993; Singh et al., 1978; Zoffoli et al., 2009). For the GA3+CPPU
treatment the detaching effect of the GA3 was presumably cancelled by the
capacity of the CPPU to thicken the rachis and pedicels and strengthen berry
attachment therefore reducing post-harvest shatter (Ben-Arie et al., 1998;
Navarro et al., 2001; Retamales et al., 1995).
In 2014, the second year of the experiment, the management of the
commercial block at Scattaglia Growers and Shippers LLC changed and
viticulture practices differed from 2013. Girdling was performed on all vines
before fruit set during 2014, despite this practice not being recommended for
Scarlet Royal (Hashim-Buckey and Ramming, 2008). Numerous authors proved
that girdling vines results in larger berries compared to ungirdled vines
(Dokoozlian et al., 1999; Reynolds and De Savigny, 2004; Winkler, 1962). The lack
of significant differences between the application of PGR and the control might
be a result of the effect of girdling masking the effect of both GA3 and CCPU
regarding berry enlargement.
47 47
Finally, the results show that the mean TA for the control and the PGR
treatments was higher than the 5.5 g/L value described for Scarlet Royal by
Hashim-Buckey and Ramming (2008). Several management and viticultural
practices can cause elevated TA values such as excessive soil moisture during
growth stage III, reduced cluster exposure to sunlight at veráison and high crop
load (Jackson and Lombard, 1993).
CHAPTER 5: CONCLUSION
Gibberellic acid and CPPU were applied to Scarlet Royal table grapes to
determine the effect on post- harvest quality parameters as well as disease
incidence. Gibberellic acid was applied at a concentration of 5 ppm and in
combination with CPPU at a concentration of 5 ppm of GA3 and 6 ppm of CPPU.
The different treatments had no effect on the incidence of Botrytis cinerea or any
other fungal disease or quality parameter tested. Moreover, PGR applications
had no effect on berry length, weight, firmness, berry skin color, titratable
acidity, total soluble solids or pH. However, berry shatter was significantly
increased by the application of GA3.
The weather conditions for the 2013/14 production years were abnormal
for the Fresno area, receiving no rain in the months of August and September.
Consequently, field conditions for mold development were not optimal and
further research is necessary to understand the effects of PGR applications on
Botrytis cinerea during post-storage.
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APPENDIX: TABLE GRAPE TYPES: SURFACE AREA IN HECTARES BY VARIETY AND YEAR PLANTED IN
CALIFORNIA
58
Table Grape Types: Surface Area in Hectares by Variety and Year Planted in California,
(CDFA, 2014).
Variety 2005 &
Earlier
2006
2007
2008
2009
2010
2011
2012
2013
2013
Bearing Non-
Bearing
Total
Arra 127 0 0 6 0 0 0 4 4 133 8 141
Autumn King 26 32 204 267 214 409 213 187 29 1152 428 1580
Autumn Royal 1542 60 33 57 25 25 24 47 28 1745 99 1845
Autumn Seedless 27 8 8 0 15 0 0 0 0 58 0 58
Beauty Seedless 80 0 0 0 0 0 0 0 1 58 1 81
Black Monukka 31 0 0 0 0 0 0 0 0 81 0 31
Black Morocco 117 0 0 0 0 0 0 0 0 31 0 117
Blanc Seedless 123 0 29 0 0 0 0 0 0 117 0 153
Calmeria 220 0 3 0 0 0 0 4 0 153 4 228
Castlerock Red 13 0 61 0 0 0 0 0 0 224 0 74
Christmas Rose 120 0 0 0 0 0 0 0 0 74 0 121
Concord 41 0 0 3 0 4 0 0 1 121 2 50
Crimson Seedless 4553 85 89 96 142 17 0 16 0 48 16 5021
Early Muscat 32 0 0 0 0 0 0 0 0 5005 0 32
Early Sweet 34 0 0 0 0 0 0 0 0 32 0 34
Emerald Seedless 153 12 6 22 13 10 0 0 0 34 0 217
Emperatriz 32 0 0 0 0 0 0 0 0 217 0 32
Emperor 201 0 0 0 0 0 0 0 0 32 0 201
Fantasy Seedless 265 0 0 9 6 2 0 28 2 201 31 315
Flame Seedless 6824 93 88 60 132 63 85 35 3 7272 122 7394
Flame Tokay 62 0 27 0 0 0 0 0 0 89 0 89
Flaming Red 45 0 0 0 0 0 0 0 0 45 0 45
59
Golden Globe 132 0 0 0 0 0 0 17 0 132 17 149
Jade Seedless 31 0 0 0 0 0 0 0 0 32 0 31
Kyoho 31 1 0 0 0 2 0 0 0 34 0 34
Luisco 13 0 15 15 8 51 20 59 15 104 95 198
Malaga 23 0 0 0 0 0 0 0 0 23 0 23
Marroo Seedless 40 0 0 0 0 0 0 0 1 40 1 41
Muscat Flame 17 0 0 0 15 212 0 0 0 244 0 244
Niabell 19 20 0 0 1 0 0 0 0 39 0 39
Nicolo 17 0 0 0 8 0 0 0 8 24 8 32
Olivette Blanche 4 0 0 0 0 6 0 15 0 10 15 24
Perlette 400 14 0 0 0 0 0 0 0 414 0 414
Prime Black
Seedless
31 0 0 0 0 0 0 0 0 31 0 31
Princess 862 323 56 47 27 41 8 13 19 1358 41 1399
Red Globe 3975 51 67 56 78 93 76 15 39 4327 129 4456
Ribier 85 0 0 0 0 0 0 0 0 85 0 85
Rouge 186 0 0 0 0 0 0 0 0 187 0 187
Royal Black
Seedless
22 0 0 0 0 12 0 0 0 23 0 23
Ruby Seedless 936 31 0 0 0 1 57 0 0 969 57 621
Scarlet 18 58 189 17 0 1 0 0 27 283 27 310
Scarlet Royal 65 199 217 491 166 362 166 132 34 1524 307 1831
Sugranineteen 114 66 119 0 0 0 0 0 0 299 0 299
Sugraone 1754 125 151 54 70 131 27 19 34 2301 68 2369
Sugrasixteen 27 0 0 0 0 7 0 0 0 34 0 34
Sugrathirteen 137 0 39 0 0 0 0 0 0 176 0 176
Summer Royal 198 71 67 13 9 7 5 17 4 365 26 391
60
Sweet
Celebration
0 0 0 0 1 134 21 85 0 136 106 242
Sweet Scarlet 43 27 0 0 66 30 0 0 0 166 0 166
Sweet Sunshine 0 0 0 0 40 0 0 0 0 40 0 40
Thomcord 0 0 4 0 0 6 5 2 9 10 16 26
Timco 8 0 0 0 8 0 22 43 31 16 95 111
Tudor 4 0 0 0 0 0 0 0 16 4 16 21
Vintage Red 93 8 8 94 55 48 94 19 55 333 168 501
90-3618 74 0 0 0 29 0 0 0 0 103 0 103
Other Varieties 171 200 182 215 141 582 380 474 106 3038 960 3998
Total Varieties 25740 1492 1681 1538 1270 2244 1205 1231 466 34047 2865 36912
The underlined varieties represent the 12 major varieties in California.
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