Effects of vernalization, photoperiod, and temperature on phenological development and spikelet number of Australian wheat

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EFFEC TS O F V ER N A LIZA TIO N , PH O TO PER IO D , A N D TEMPER A TU R E

O N PH EN O LO G IC A L D EV ELO PMEN T A N D SPIK ELET N U MB ER

O F A U STR A LIA N W H EA T

By

N. J. HALSE

nd R. N. WEIR*

[Man uscript received December 10, 19691

Summary

Sixteen Australian wheat cultivars grown in controlled environment cabinets

demonstrated a range of responses to seed vernalization varying from little or no pro-

motion of floral initiation in Darkan, Kondut, Falcon, and Sunset to about 3 weeks in

Festiguay, Claymore, and Mexico 120. Under short days (10 hr photoperiod v 14 hr)

or cold temperatures (12/7 C daylnight v. 18/13 ) the response to seed vernalization was

reduced. None of the cultivars responsive to vernalization achieved floral initiation

earlier under cold temperatures than under warm temperatures, even in the absence o

seed vernalization. All cultivars achieved floral initiation earlier in long days but the

magnitude of the response varied considerably among them. Long days similarly

accelerated development from initiation to anthesis.

Higher temperatures accelerated development to initiation and anthesis in all

cultivars, with only minor differences in magnitude of response.

Selected treatments in the cabinets gave rates of development to initiation which

closely paralleled results for the same cultivars in field experiments.

The number of spikelets per head varied considerably with cultivar, day length,

and vernalization treatment. Within the range of conditions of the experiments, tem-

perature did not affect spikelet number other than through vernalization. At either

temperature, the spikelet number was closely and positively related to the number of

days to floral initiation.

Wheat is normally grown in Australia under climatic conditions in which the

growing seaso n is limited by the period of effective rainfall. Successful com mercial

wheat cultivars must complete their development to grain m aturity w ithin this restricted

period. The phenological development of Australian w heats is partly governed by

climatic environment, and specific influences of day length and vernalization have

been reported G ott 1961 Pugsley 1963, 1966) as well as the multiple influences of

sowing time Aitken 1966; Syme 1968).

Th e economic importanc e of phenological development in wheat is not restricted

to the duratio n of the growth period. Env ironm ental conditions can produce different

patterns of development leading to changes in the times of processes such as floral

initiation. Co nditions before or during floral initiation can affect the size and n umber

of spikelets on the spike Friend 1 965; Th orn e, Ford , and Watson 1968) an d this can

directly affect yield.

It has been suggested that wheat cultivars which respond to vernalization may

have som e advantages in escaping frost G ot t 1961) bu t the actual effect of field

Western Australian Department of Agriculture, South Perth, W.A. 6151.

Aust J agric

Res.

1970,21 383-93



3

84 N.

J.

HALSE AND R.

N.

WEIR

vernalization has no t been estimated fo r Au stralian wheat cultivars. In the experiment

described, an assessment was m ade of the significance of vernalization by co ol winter

tem peratures in the vegetative plant. The experiment examined the phenological

responses of a wide range of cultivars to precise differences in the enviro nm ent in term s

of day length and temperature, and comparisons were ma de of phenologieal develop-

me nt unde r these cond itions with observations m ade o n field experiments in the W estern

Au stralian wh eat-belt. Finally it was intended to determine the effect of environ-

me ntal factors on spikelet numb er a n d whether such effects were related to the rate of

development.

11. METHODS

The cultivars included in the experiment are listed in Table 1. Apart from

Sun set all are in comm ercial use in Western Au stralia. Mexico 120, the only non-

Australian wheat, has been tested widely in Australia and has been frequently used in

breeding programmes.

T BLE

CULTIV RS

USE

IN THE EXPERIMENT

Breeding

Name

Organization

Parentage*

Bencubbin

Claymore

Darkant

Emblem

Falcon

Festiguay

Gabo

Gamenya

Gamut

Heron

Kondut

Mendos

Mexico 120P

Noongar

Sunset

Wagin

Dep. Agric., W.A.

Roseworthy Agric.

College, S.A.

Dep. Agric., W.A.

Dep. Agric., Vic.

Dep. Agric., N.S.W.

Dep. Agric., N.S.W.

Sydney University

Sydney University

Sydney University

Dep. Agric., N.S.W.

Dep. Agric., W.A.

Sydney University

Cimmyt, Mexico

Dep. Agric., W.A.

Dep. Agric., N.S.W.

Dep. Agric., W.A.

Nabawa x Gluyas Early

Gabo x Dundee x Caliph)

Unknown cross

x

Kenya C6041 x Eureka 11)

Ghurka

x

Pusa 1V)

x

Insignia)

x

Insignia 658

Gular x Dundee x Gular)

x

Bencubbin

Festival x Uruguay C10837

Bobin seln. Gular?)

x

Gaza x Bobin seln. Gular?)

Gabo x Gabo5 x Mentana) x GaboZ x Kenya

117A)

Gamenya x Gabo

x

Kenya 324

x

Urquiza)

Ranee

x

Doubbi

x

Ranee

x

Insignia x

Insignia 493

Wilfred

x

Sutton

Spica x Koda)

x

Gabo)

x

Mengavi Sib.

Yaktana 54 x Norin Brevor 21-1C

Sunset

x

Gluyas Early

Blounts Lambrigg Sport

x

Fife x Summer Club)

Doubbi x Gabo)

x

Ben~ubbin)~

From Macindoe and Walkden Brown 1968).

f

Information supplied by

J.

T. Reeves, Dep. Agric., W.A.

Th e wheat plants were grown in type

LB

artificial light cab inets (Pescod, R ead ,

and Cunliffe 1963), with a 2 x

2

x 2 factorial combination of the following

treatments

Tem perature: 18°C day,

13

night

(H)

v

12 day,

7

night

(C),

Photoperiod: 14 hr (L) v 10 hr (S),

Vernalization: Seed vernalized (V) v nil 0) .



PHENOLOGICAL DEVELOPMENT OF AUSTRALIAN WHEATS

385

The eight treatm ents were imposed o n 16 cultivars in duplicate pots with eight

plants per pot. The plants were grown in quartz grit an d supplied with a full nutrient

solution. The growing conditions provided a high light intensity day with fluores-

cent and incandescent light at 3000 f.c. (Weston sunlight illumination meter, not

cosine-corrected) for 9 . 5 hr. Day tem peratures were maintained fo r this period.

Th e day length was extended for 0 .5 h r an d 4 . 5 hr with low intensity incandescent

light in the sh ort an d long day treatments respectively. Th e period u nder high light

intensity was adjusted slightly to achieve equa l total energies in the visible wavelength

range for the two photoperiod treatments.

The environmental treatments were chosen to represent the extreme conditions

under which wheat is grown comm ercially in Western Au strali a. The warm est growing

conditions would be for early-planted wheat a t Chap man (north of Geraldton) an d the

coldest would be a t W anderin g. Th e conditions in these situations are set out below:

Chapman Warm Wandering Cold

(June) Cabinet H) (July) Cabinet (C)

The du al temp erature regime in the phytotron is regarded as a reasonable integration

of diu rnal fluctuation.

The day lengths of 10 and 14 hr are respectively similar to the shortest day

length (June) and longer than th e longest (abou t 1 2. 5 hr) in September-October for

very late-planted crops on the south coast.

Seed vernalization was carried out by the method of limited water content as

used by G ott (1961). Th e seed was kept at 3 4 ° C for a period of

6

weeks with the

water content at

c.

55

.

Max. temp. ( C)

Min. temp. ( C)

Mean temp. ( C)

Plants were sampled and dissected at intervals to determine the initiation time

fo r each treatme nt. Th e development of the primary sho ot of these plants was scored

or,

a

system similar to t ha t of Friend, F isher, and H elson (1963). O n this scale (0,

commen cement of germ inatio n; 100, anthesis) the first visible sign of axillary bud

developmen t (spikelets) on the apex of the ma in sho ot (score 32) was regarded a s floral

initiation. This stage is slightly earlier than that of typical double ridges (Bonnett

1936). Th e scores of successive samples from a ny treatm ent, plotted against time,

enabled a regression line t o be calculated. Th e intercept of the regression line with the

score 32 was taken as the time to initiation.

1 9 . 8 1 8 . 0

15 . 1

12.0

9 . 0

1 3 . 0 3 . 9

7 . 0

1 4 . 4

1 5 . 0

9 . 5 9 . 0

Four plants were left unsampled in each treatment and the times of anthesis

(first visible extrusion or dehiscence of anthers) recorded for the main shoot of each

plant. Th e spikelet num bers were determined on the same heads.

Field trials not reported here in detail were carried out at the Wongan Hills

Research S tation of the Western Australian D epartm ent of Agriculture in 1967 and

1968, with the same cultivars as in the principal experiment. These experiments were

planted on Ju ne 8 and J un e 24 respectively into m oist soil. Th e time of floral initiation

was determined by a similar method to that described above.



N. J. HALSE AND R. N. WEIR

a ) Vernalization Response

The results are expressed only in terms of the reduction in the interval from

germ ination to floral initiation. Time fro m initiation to anthesis was generally no t

affected by vernalization. Full results fro m all treatments on the time to initiation are

included in an Appendix? In Table 2 the response t o seed vernalization is shown fo r

warm long days HL) where no modification of the response by environm ental verna-

lization would be expected for warm sh ort days

HS)

where any effect of short day

induction should be present and for cold long days CL) where vernalization of the

youn g plants by ambient temperatures c ould occur. Th e cultivars in Tab le 2 are

arranged approximately in order of response. The group from Bencubbin to Claymore

which gave the biggest response to vernalization showed considerably less response

in short days and cold temperatures.

PROMOTION OF INITIATION

BY SEED

VERNA- PROMOTION OF INITIATION A N D OF

LIZATION Iii PLANTS GROWN AT:

ANTHESIS

OF

VERNALIZED

PLANTS BY

18/13 C, 14 HR DAY (HL)

LONG PHOTOPERIODS (14 HR)COMPARED

18/13 C, 10 HR DAY (HS)

WITH

SHORT

PHOTOPERIODS (10 HR)

12/7 C, 14 HR DAY (CL)

Results are means of both temperatures

Cultivar

Sunset

Falcon

Kondut

Darkan

Noongar

Wagin

Gamut

Mendos

Gabo

Gamenya

Bencubbin

Emblem

Heron

Festiguay

Mexico

Claymore

Promotion of

Initiation (days)

Cultivar

Sunset

Noongar

Darkan

Mexico

Gamenya

Mendos

Gamut

Claymore

Wagin

Gabo

Heron

Falcon

Emblem

Kondut

Bencubbin

Festiguay

Promotion

(days)

Initiation Anthesis

No anthesis in short photoperiod.

b )

Photoperiod Response

In Tab le the prom otion of initiation and anthesis by long photoperiods is shown

on vernalized plants. The effect of photo period is mo re validly estimated on vernalized

Copies of this Appendix are available on application to the Editor-in-Chief, Editorial and

Publications Section, CSIRO, 372 Albert Street, East Melbourne, Vic. 3002.








389

same treatment. In order to examine this relationship, spikelet num bers for all treat-

ments for which they were available) were plotted against time to initiation.

Completely different relationships were apparent f or the two tem perature con-

ditions. In addition, th e cultivars which showed a large response to vernalization had

TABLE

SPIKELET

NUMRFR

PPF PRIW RY

BEAE

S F

SEED

VERNALIZED PLANTS, SHOWING THE

MEAN

EFFECT OVER

BOTH TEMPERATURES OF LONG

L)

A N D

SHORT S)

PHOTOPERIODS

Cultivar

Sunset

Noongar

Darkan

Mexico

Gamenya

Mendos

Gamut

Gabo

Falcon

Spikelet Number

L S

14.6 20.1

1 5 . 2

1 9 . 5

15 .9 22 .9

14 .7 20 .2

18.0 24.4

17 .1 24 .4

16 .1 24 .9

15 .5 21 .1

17 .4 22 .4

LSD between any means: P

0.05

1.9

P

0 .01 2 .5

a lower spikelet number when they had not been seed-vernalized than would be ex-

pected from their time to initiation. T hese cultivars group

B)

were Bencubbin, Emblem,

Hero n, Festiguay, Mexico, and Claymore. Regressions of spikelet num ber on time t o

initiation were calculated for the four groups two groups x two temperatures).

I

15 20

25

30

35

40 45 50

Days

to initiation

Fig. 1

-Regression lines

of spikelet number on

days to initiation at high

and low temperatures,

both for

all

cultivars and

for those highly responsive

to vernalization when not

seed-vernalized group

B).

There was a significant regression fo r each group of figures Fig.

1).

The four groups

did no t differ significantly in slope bu t the two temperatures and two cultivar groups

differed significantly in position.



390 N. J H LSE ND R N. WEIR

IV. DISCUSSION

Where comparisons are possible, the ranking of the wheat cultivars tested for

vernalization response agrees with those of other workers. G o tt (1961) obtained

similar results for Bencubbin, Ko ndu t, and Ga bo, an d altho ugh Syme (1968) found

little vernalization response in Heron, he suspected that the response may have been

underestimated.

I t is difficult to assess the degree to w hich cold tem pera tures vernalized the grow-

ing plants. Th e plants in cold conditions were exposed to an a ir temperature of 7°C

for 14 .5 h r per day. Purvis (1948) fou nd n o difference between

l o

nd

7

for vernalizing

rye, while Ch ujo (1966) concluded tha t daily alterna ting temperatures with 10 as a low

tem pera ture were effective with wheat. Th is means th at plants und er cold conditions

in the experiment would have been under vernalizing conditions. Although the res-

ponse t o seed vernalization was less und er low tha n high grow ing temperatures for the

most responsive cultivars (Table 2) these cultivars, even when unvernalized, achieved

initiation a s quickly und er high as under low growing temperatures. Clearly the

degree of winter hab it present in the tested Australian wh eat cultivars is no t enough

to counterbalan ce their acceleration by warm growing conditions.

T he differences between cultivars in respo nse to day leng th were substantial, and

reasonably similar for the pre-initiation and post-initiation stages in contrast to the

results o btain ed by G o tt (1961), who foun d little effect of day length on post-initiation

developm ent. In the present experiment a num ber of cultivars, having initiated, failed

to complete normal emergence and anthesis in sh ort photoperiods. The heads of these

cultivars senesced or abo rted within the leaf sheaths. Alth oug h this has been observed

previousIy (Forste r

et

al 1932; Pugsley 1966) it does not a pp ea r comm on with Aus-

tralian c ultivars in da ys as long as 10 hr.

The observations on photoperiod were based on vernalized plants, to avoid

confusion with possible sh ort day induction effects. It did ap pea r tha t some cultivars

when not vernalized were earlier in initiation under short days than would otherwise

have been expected, e.g. Festiguay (Table 2). Th e position was rather similar to that

with plant vernalization: neither sho rt days nor cold tem peratures actually advanced

initiation in unvernalized responsive cultivars, but they did not delay initiation as

happened with vernalized plants. A possible explanation could be tha t where lack of

vernalization delayed floral initiation, the time taken to overcome this was not fully

additive to delays due to sh ort photoperiod o r low temperature.

Althoug h the response to higher temperature in tim e to initiation and anthesis

was large, the differences between cultivars did not follow the same pattern for both

periods. F o r this reason n o attem pt is made to assign any real significance to differ-

ences between cultivars.

On the basis of the responses to vernalization and photoperiod observed. a

general classification of the cultivars includ ed in the experim ents is presented in Tab le

8.

The classification does not represent the f ~ d lange of responses possible. European

cultivars like Jufy

I

are more sensitive to photoperiod than any in this experiment

(Syme 1968) while the North American wheat Cheyenne and the Australian wheat

Winter Minflor are more sensitive to vernalization (Gott 1961). Where cultivars are

shown a s ove rlapping two categories, this is because d at a were insufficient to determine



PHENOLOGICAL DEVELOPMENT

O F

AUSTRALIAN WHEATS

39

their true position. I t is suggested that such a table can be of use in predicting the

probab le response of different cultivars in phenological development to any alteration

in environment.

TABLE

CLASSIFICATIONOF

USTR LI N

WHEAT CULTIVARSBASED ON

THEIR

OBSERVED

RESPONSES TO VERNALIZATION AND TO CH NGES IN PHOTOPERIOD

ncreasing vernalization response

-

Sunset

-

Falcon

The use of data from artificial environments for predicting field behaviour is

supported by the close agreement obtained with data from Wongan Hills Research

Station Table 5). July temperatures at Wongan Hills are: mean monthly minimum

5.6 C, ean monthly maximum 15.6 . The effective day length for photoperiod is

between 1 and

11

hr. Although it is nearly impossible to duplicate a field environ-

ment in artificial conditions, the results suggest that by selecting cond itions based on

those in the field such plant responses as phenological development can be reliably

predicted.

Temperature, photoperiod, and vernalization all affected the phenological de-

velopment ra te in sensitive cultivars but their effects on spikelet num ber per primary

head were quite different. Increases in time to in itiation caused by s ho rt photoperiods

were associated with increased spikelet num bers; increases caused by lack of vernal-

ization were likewise associated with increases in spikelet num ber ; bu t increases in

time to in itiation caused by low temperatures were not accompanied by any significant

change in spikelet num ber. The latter result differs from that of Friend (1965), who

found a curvilinear relationship between temperature an d spikelet number. The

two temperatures used in the present experiment may have been situated on opposite

sides of a peak, and its existence would thus fail to be detected. Th at temperature

might not have the same effect as photoperiod and vernalization could be explained

by its general effect on all growth processes. Delays in development t o the stage of

initiation were associated with reductions in growth rate at the temperatures tested.

Although leaf number was not measured in this experiment, unpublished data from

Kondut

~e s t i g u a y

Bencubbin

Darkan

Emblem

Heron

Noongar

amenya

Mendos

Gamut

Wagin

Gabo

Mexico

Claymore



392 N. J.

HALSE AND R.

N. WEIR

similar experiments carried out by the authors have shown similar leaf numbers at

different temperatures. This would suggest tha t th e leaf emergence rate is affected to

the same extent by temperature as development to flowering.

Th e correlation between time to initiation an d spikelet number Fig. 1) is of con-

siderab le interest since it includes the differences between cultiva rs. I t might be con -

sidered th at this correlation su ppo rts the co ntentio n that po tential spikelet num ber is

determined by the time of initiation Thorne, F ord , and Watson 1968). T he results

obta ined by Friend 1965) indicated that spikelet num ber could be determined by

con ditions after initiation an d this accords with the suggestions for wheat Williams

1966) an d barley Nicholls an d M ay 1963) th at the relative rates of primordium

form ation an d spikelet development determine the final spikelet num ber. We would

suggest that spikelet number is at least partly determined by the time of initiation,

depending on the number of primordia present at that stage on the primary apex.

However, subsequent conditions may also influence it and the high correlations

obta ined here may be due t o a linkage of time to initiatio n with the actual determ ining

con ditions . Th e variation in correlation for unvernalized cultivars can not be ex-

plained on the data at present available.

Th e agricultural significance of factors affecting spikelet nu mber on the primary

shoo t lies in its effect o n grain num ber. Despite the frequent dem onstration of the

impo rtance of photosynthetic area Thorne and Watson 1955; Fischer and Ko hn

1966) grain number is a yield determinant in some situations Thorne , Ford, an d

W atso n 1968). Th e spikelet number per head is one of a series of factors including

number of heads per acre, florets per spikelet, and floret fertility) which determine

grain nu mb er. In breeding o r selecting wheats for specific environmen ts, use could be

m ad e of know n responses of wheat cultivars to select o r prod uce ones which developed

a high spikelet number for the am bient conditions.

The considerable assistance of Miss Helen Nicol in the statistical treatment of

results and the technical assistance of Miss E. Tru e and M r. G . G regory is gratefully

acknowledged.

VI. REFERENCES

AITKEN, VONNE1966).-Flower initiation in relation to maturity in crop plants.

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445-51.

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G.

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281-95.

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. C.

VASEY,

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J., TINCKER,M. A. H., and WADHAM,. M . 1932).-Experiments in

England, Wales and Australia on the effect of length of day on various cultivated varieties of

wheat. Ann. appl. Biol. 19 378412.

FRIEND, .

J. C.

1965).-Ear length and spikelet number of wheat grown at different temperatures

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J.

Bot. 43 345-53.




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FRIEND,D.

J. C .

FISHER,

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and HELSON,

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1963)-The effect of light intensity and tem-

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PESCOD,

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578-81.

THORNE, ILLIANN., FORD,MARGARET., and WATSON, .

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Documents

Effects of vernalization, photoperiod, and temperature on phenological development and spikelet number of Australian wheat