Factors affecting the nematicidal activity of dimethyl

J. Alfonso Cabrera1,2*, Jay Gan2, Bradley D. Hanson1,3, and Dong Wang1

1Water Management Research Unit, USDA-ARS, Parlier, CA 93648, USA. 2Department of Environmental Sciences, University of California, Riverside, CA 92521, USA. 3Department of Plant Sciences, University of California, Davis, CA 95616, USA.

*E-mail: [email protected]

November 2nd, 2010Orlando, Florida

Factors affecting the nematicidal activity of dimethyl disulfide (DMDS)

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INTRODUCTION

California has around 350,000 ha planted with raisin, table, and wine grapevines (Cline, 2006)

A common agricultural practice in this area is to replant the grapevines after each cropping cycle

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INTRODUCTION

Several replant problems are often encountered when replanting

Citrus nematodes (Tylenchulus semipenetrans) is often encountered in replanted grapevines

(Cabrera and Wang, 2010)

(Mai and Lyon, 1975)Second-stage female larva

This nematode can reduce the grapevine development and the overall productivity

(Ferris and McKenry, 1975; McKenry, 1992; Nicol et al., 1999; Rahman et al., 2008)

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Crop Critical condition (EPA, 2010)

Raisin, table and wine grapes Moderate to severe nematode infestationModerate to severe soilborne disease infestationReplanted orchard soils to prevent orchard replant diseasePresence of medium to heavy soilsLocal township limits prohibiting 1,3-dichloropropene

INTRODUCTION

Methyl bromide (Mbr) was used to control citrus nematodes and other soilborne pest and pathogens in the replant problem

However, Mbr is being phased-out and can be used only as a Critical Use Exception (CUE)

CUE for Mbr pre-plant fumigation in California grape production:

INTRODUCTION

Dimethyl disulfide (DMDS) is a sulfur volatile product that can be produced commercially from acid natural gas (Gillis, 2003; Kubec et al., 1998)

DMDS:

When DMDS is produced by a plant it may be as a mechanisms of defense against plant pathogens (Auger and Charles, 2003)

Commercially produced, is a relatively new compound in agriculture that has zero ozone depletion potential (Gillis, 2003)

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INTRODUCTION

DMDS can be well delivered through shank injection and by using drips systems (Charles, 2003; Fritsch, 2005; Heller et al., 2009)

Shank injection Drip system

Gas DMDS emissions can be reduced by around 42% when soil moisture content is 10% in sandy and loamy sand soils (Sumner and Culpepper, 2008)

The degradation of DMDS can be biologically mediated (Cho et al., 1991)

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INTRODUCTION

DMDS is highly effective against plant parasitic nematodes:

•DMDS applied at 300 kg a.i./ha was highly effective reducing gall index in tomatoes, and juveniles in soil of Meloidogyne incognita, and M. javanica as well as Heterodera schachtii cysts using sugar beets (Charles, 2003)

• Shank injected DMDS reduced penetration of Pratylenchus penetrans and M. hapla to strawberries (López-Aranda et al., 2003)

•DMDS applied at 785 kg/ha reduced the root gall ratings in an ornamental plant (Celosia argentea var. cristata) and juvenile contents in soil of Meloidogyne spp. (Rosskopf et al., 2006)

•DMDS reduced the populations of Tylenchulus semipenetrans in soil (Wang et al. 2009; Mejorado et al. 2010; Hanson et al. 2010)

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species

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INTRODUCTION

However, the factors that affect the nematicide activity of DMDS have not been investigated in detail

If DMDS could be applied as post-planting treatment, in cases as in grape production systems to control nematodes requires investigation

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OBJECTIVES OF THE STUDY

1.To determine the sensitivity of citrus nematodes to DMDS

2.Evaluate the effect of time of exposure, soil moisture and temperature on DMDS efficacy

3.Compare the efficacy of DMDS in two different soil types

4.Evaluate different DMDS dosages as post-planting treatment under microplot and field conditions in established grapevines

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MATERIALS AND METHODS1. To determine the sensitivity of citrus nematodes to DMDS:

•11 ml nematode suspension containing 10 active citrus nematodes/ml tap water was prepared

• DMDS analytical grade (Sigma Aldrich) was applied to the nematode suspension at 0, 32, 64, 128, or 256 mg a.i./L final concentration.

•Every vial was caped with an aluminum seal cap with silicone septa (A) and incubated horizontally (B) in a rotator under dark conditions at 26°C (C).

• A 2 ml sample was taken with a stainless steel needle (D) 3, 6, 24, and 192 h after DMDS application(E).

•The number of active, inactive and dead nematodes in every sample was determined as described by Faske and Starr (2006) under a microscope.

A B C D E

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RESULST1. To determine the sensitivity of citrus nematodes to DMDS:

Effect of different DMDS dosages on citrus nematode survival at different exposure times

T-test (p<0.05), * = significant different, N.S. = not significant differentOne-way ANOVA test (p<0.05), Letters indicate differences among treatments according to Fisher’s least significant difference testError bars indicate standard error of the mean valueN = 3

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MATERIALS AND METHODS2. Evaluate the effect of time of exposure soil moisture and temperature on DMDS

efficacy:

•DMDS at 0, 32, 64, 128 or 256 mg a.i./L air space

•Evaluated at 6, 24, 96 and 192 h

A B C

A) Citrus nematode naturally infested soil (400 nematodes/100 ml soil) B ) Vials with soil and DMDSC) Extraction of nematodes using the Baermann funnel technique

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MATERIALS AND METHODS2. Evaluate the effect of time of exposure, soil moisture and temperature on DMDS

efficacy:

•10, 30 and 60% water holding capacity (WHC)

•DMDS at 0, 32, 64, 128 or 256 mg a.i./L air space.

10% 30% 60%WHC

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MATERIALS AND METHODS2. Evaluate the effect of time of exposure, soil moisture and temperature on DMDS

efficacy:

•9, 26 and 37˚C

•DMDS at 0, 32, 64, 128 or 256 mg a.i./L air space

9˚C 26˚C 37˚C

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RESULTS2. Evaluate the effect of time of exposure, soil moisture and temperature on DMDS

efficacy:

0

20

40

60

80

100

120

0 32 64 128 256

Effic

acy

(%) o

n ci

trus

nem

atod

es

Dimethyl disulfide dose (mg a.i./L a.s.)

Exposure time6h24h96h192h

One-way ANOVA test (p<0.05), Circles indicate differences among treatments according to Fisher’s least significant difference testError bars indicate standard error of the mean valueN = 4

A) Effect of exposure time on DMDS efficacy

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efficacy:

0

20

40

60

80

100

120

0 32 64 128 256

Effic

acy

(%) o

n ci

trus

nem

atod

es


Exposure time6h24h96h192h

0

20

40

60

80

100

120

0 32 64 128 256

Effic

acy

(%) o

n ci

trus

nem

atod

es


Soil water holding capacity10%30%60%

One-way ANOVA test (p<0.05), Circles indicate differences among treatments according to Fisher’s least significant difference testError bars indicate standard error of the mean valueN = 4

A) Effect of exposure time on DMDS efficacy B) Effect of soil moisture on DMDS efficacy

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0

20

40

60

80

100

120

0 32 64 128 256

Effic

acy

(%) o

n ci

trus

nem

atod

es


Temperature of incubation9°C26°C37°C


efficacy:

One-way ANOVA test (p<0.05)Error bars indicate standard error of the mean valueN = 4

C) Effect of temperature on DMDS efficacy

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MATERIALS AND METHODS3. Compare the efficacy of DMDS in two different soil types:

Hanford fine sandy loam,

collected near Parlier, CA

Traver loam soil, collected near

Madera, CAChemicalPhysical

Properties (Web Soil Survey)

Soil microbiology

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MATERIALS AND METHODS3. Compare the efficacy of DMDS in two different soil types:

Hanford fine sandy loam,

collected near Parlier, CA

Traver loam soil, collected near

Madera, CAChemicalPhysical

Properties (Web Soil Survey)

Soil microbiology

Soils were tested with the same moisture content (30% WHC)Same time of incubation (192 h)Same temperature (26 ˚C)A suspension containing active juvenile citrus nematodes was inoculatedDMDS application

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RESULTS3. Compare the efficacy of DMDS in two different soil types:

0

20

40

60

80

100

120

0 32 64 128 256

Effic

acy

(%) o

n ci

trus

nem

atod

es


Soil typeHandford fine sandy loam Traver loam

Efficacy of DMDS on citrus nematodes in two different soil types

Circles indicate differences according to T-test (p<0.05) Error bars indicate standard error of the mean valueN = 4

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CONCLUSIONS

1. Citrus nematodes are highly sensitive to low dosages of DMDS (32 mg a.i./L), in particular after 24 hours of exposure or more

2. DMDS at 256 mg a.i./L can greatly affect nematode behavior within 3 hours in 75% of the population

3. Time of exposure and soil moisture content can affect DMDS efficacy, in particular at low dosages

4. Temperature did not play a major roll in DMDS efficacy

5. At low dosages DMDS efficacy may significantly vary among soils whereas at higher rates the soil type is less important

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FURTHER RESEARCHEvaluate the efficacy of DMDS in micro-plot and field conditions

J. Alfonso Cabrera1,2*, Jay Gan2, Bradley D. Hanson1,3, and Dong Wang1

1Water Management Research Unit, USDA-ARS, Parlier, CA 93648, USA. 2Department of Environmental Sciences, University of California, Riverside, CA 92521, USA. 3Department of Plant Sciences, University of California, Davis, CA 95616, USA.

*E-mail: [email protected]

November 2nd, 2010Orlando, Florida

Factors affecting the nematicidal activity of dimethyl disulfide (DMDS)

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Many thanks for your attention

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Factors affecting the nematicidal activity of dimethyl