variation in pod production and abortion among chickpea cultivars under terminal drought

Europ. J. Agronomy 24 (2006) 236–246

Variation in pod production and abortion among chickpeacultivars under terminal drought

L. Leporta,1, Neil C. Turnera,b,∗, S.L. Daviesa,c, K.H.M. Siddiquea

a Centre for Legumes in Mediterranean Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australiab CSIRO Plant Industry, Private Bag No. 5, Wembley, WA 6913, Australia

c Western Australian Department of Agriculture, PO Box 110, Geraldton, WA 6531, Australia

Received 12 October 2004; received in revised form 5 July 2005; accepted 2 August 2005

Abstract

The effect of terminal drought on the dry matter production, seed yield and its components including pod production and pod abortion wasinvestigated in chickpea (Cicer arietinum L.). Two desi (with small, angular and dark brown seeds) and two kabuli (with large, rounded and lightcoloured seeds) chickpea cultivars differing in seed size were grown in a controlled-temperature greenhouse, and water stress was applied bywithholding irrigation 1 (early podding water stress, ES), 2 (mid-podding water stress, MS) or 3 (late-podding water stress, LS) weeks after thec et. Growtho arly seedg ving fewers branches waso branches werem ion was mores inal droughtc results showt ferences inpC

K

1

ttScmBra

I

2con-ao999;t

ckagesses.eno-

roundrain-from

eno-in

mberes notvar of

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ommencement of pod set. In addition, the pod and seed growth of well-watered plants was followed for the first 19 days after pod sf the pod wall followed a sigmoid pattern and was faster in the desi than in the kabuli cultivars, while no difference was found in erowth among genotypes. Time of pod set affected the yield components in all treatments with the late-initiated pods being smaller, haeeds per pod and smaller seeds, but no significant difference between pods initiated on the same day on the primary and secondarybserved. Early stress affected biomass and seed yield more severely than the later stresses, and in all stress treatments secondaryore affected than primary ones. Pod production was more affected by early stress than by late stress, regardless of cultivar. Pod abort

evere in the kabuli than in the desi cultivars, but final seed size per se did not appear to be a determinant of pod abortion under termonditions. The data indicated that the production and viability of pods was affected as soon as water deficits began to develop. Thehat pod abortion is one of the key traits impacting on seed yield in chickpeas exposed to terminal drought and that irrespective of difhenology, kabuli types have greater pod abortion than desi types when water deficits develop shortly after first pod set.rown Copyright © 2005 Published by Elsevier B.V. All rights reserved.

eywords: Cicer arietinum L.; Seed growth; Pod growth; Water relations; Pod abortion; Seed abortion; Kabuli and desi chickpea

. Introduction

There are two types of chickpea (Cicer arietinum L.): (i)he small-seeded desi chickpea with a dark and thick seed coat,hat is split and the kernel used for dahl or flour primarily inouth Asia, and (ii) the large-seeded kabuli chickpea with a light-oloured and thin seed coat that is used as a whole seed or in hom-us or falafal primarily in countries around the Mediterraneanasin. While disease, especiallyAscochyta blight (Ascochyta

abiei; Mycosphaerella rabiei; Didymella rabiei), is currentlymajor limitation to chickpea production in Mediterranean-

∗ Corresponding author. Tel.: +61 8 6488 4723; fax: +61 8 6488 1140.E-mail address: [email protected] (N.C. Turner).

1 Present address: Osmoadaptation and Stress Metabolism, UMR CNRS 6026CM, University of Rennes 1, F-35042 Rennes Cedex, France.

climatic regions (Cubero, 1984; Knights and Siddique, 200),abiotic stress, particularly terminal drought, is also a majorstraint to yield in most regions (Singh et al., 1990; Subbaret al., 1995; Thomson et al., 1997; Leport et al., 1998, 1Siddique et al., 1993, 2000; Turner, 2003). The developmenof disease resistant cultivars and disease management pawill again highlight the sensitivity of chickpea to abiotic stresIn the absence of disease, a field study with five desi gtypes and one kabuli genotype showed that total above-gbiomass did not differ among genotypes, but seed yields offed chickpeas subjected to terminal drought were reduced53 to 42% compared to those of irrigated plants in all gtypes (Leport et al., 1999). This was related to a decreasepod numbers from 44 to 30% and a decrease in seed nufrom 46 to 35% (Leport et al., 1999), but whether this was duto a reduced production or increased abortion of pods wainvestigated. A subsequent greenhouse study with one culti

161-0301/$ – see front matter. Crown Copyright © 2005 Published by Elsevier B.V. All rights reserved.oi:10.1016/j.eja.2005.08.005

L. Leport et al. / Europ. J. Agronomy 24 (2006) 236–246 237

chickpea showed that both the production and abortion of podswas reduced by a water deficit imposed after the commencementof pod set (Behboudian et al., 2001). The study byLeport et al.(1999)suggested that in addition to pod production or abortion,seed yields of chickpeas decreased because of fewer seeds perpod in some genotypes, suggesting that seed abortion can alsooccur. Under field conditionsDavies et al. (1999)showed thatterminal drought reduced the duration of seed filling, and hencethe final seed size, in three chickpea genotypes. However, seedsize under both rainfed and irrigated conditions was similar inboth the secondary and primary branches (Davies et al., 1999).

Recent studies byMa et al. (2001)andFurbank et al. (2004)have shown that the pod is an important photosynthetic organin refixing respired carbon within the pod wall that is thentranslocated to the developing seed. As the seed coat of thedeveloping seed is unaffected by water deficits in the rest ofthe plant (Shackel and Turner, 2000), the refixation of car-bon within the pod is considered to be even more importantunder terminal drought (Ma et al., 2001). The ability of thepod and seed to survive when drought occurs is an importantstep in improving yield under terminal drought. Under termi-nal drought conditions, kabuli types of chickpea have a greaterreduction in yield and pod number per plant compared to desitypes (Leport et al., 1999; Siddique et al., 1999), but it is not clearwhether this is associated with their generally later flowering andhence exposure to greater terminal stress, their greater seed size,o abut

therew rtiona entsa ed td abort theg werc r. Ap kabu l.,1 um-s ltiva( as thm e pes

2

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ds edc a(c tt trali( ngp vinyc red

loam (Calcic Haploxeralf) from the top 10 cm of a field inMerredin (Thomson et al., 1997) mixed with 1.4 kg of coarsesand. One gram of a commercial microelement preparation(Richgrow®), 7.5 g of potassium nitrate, 7.1 g of ammoniumnitrate, 10.7 g of calcium nitrate and 7.6 g of triple superphos-phate was mixed with each 50 kg of soil, corresponding to 1.4 gof N, 0.6 g of P and 0.8 g of K per pot.

2.2. Management

The plants were sown on 30 June (the usual season for plant-ing chickpeas in the southern hemisphere) in a commercialpotting mix in flat trays. All seeds were inoculated with a com-mercial Group NBradyrhizobium immediately before sowing.Three days after sowing (DAS) one seedling was transferred intoeach pot previously watered to field capacity. All pots were irri-gated commencing 3 DAS with 200 ml of water per pot everysecond day to maintain the soil near field capacity. For eachgenotype, pots were designated to one of the four groups cor-responding to four treatments: well-watered control (C), earlypodding water stress (ES), mid-podding water stress (MS), andlate-podding water stress (LS). Control plants were irrigatedevery 2 days until the ES plants reached maturity (121 DASfor Tyson, Sona, and Kaniva and 128 DAS for Narayen). Irri-gation of Tyson, Sona and Kaniva was maintained until 93,100, and 107 DAS for ES, MS and LS, respectively, beforet weekl ntil1 andt potsw sure-m hreew s thes areaa mentw seedg fourr ousew thep

2

d endo ningu ong)o d andi threew poda or thefi d set(

2

pre-v s

r other inherent genetic differences between desi and kypes.

The present study was initiated to determine whetheras any variation in pod and seed production and abomong chickpea cultivars. By imposing water deficit treatmt three stages during reproductive development, we aimetermine the stage at which a water deficit induced pod

ion. Differences in pod initiation among the cultivars inreenhouse were small and the water deficit treatmentsommenced at the same time after pod set in each cultivarevious studies have shown that pod numbers are lower inli than in desi genotypes (Leport et al., 1999; Siddique et a999), we compared pod abortion in both small- and medieeded desi cultivars and small- and large-seeded kabuli cuthe small-seeded kabuli cultivar had the same seed sizeedium-sized desi cultivar) to determine whether seed siz

e had an influence on pod abortion.

. Materials and methods

.1. Experimental design

Four chickpea (C. arietinum L.) cultivars differing in seeize, two desi types, cv. Tyson (mean seed size = 0.12 g se−1),v. Sona (0.22 g seed−1), and two kabuli types, cv. Kaniv0.42 g seed−1), and cv. Narayen (0.20 g seed−1) were grown in aontrolled-temperature greenhouse, set at 22◦C/15◦C day/nighemperatures, at CSIRO, Floreat Park, Perth, Western Aus31◦57′S, 115◦47′E). The plants were grown in free-drainiots, each made from 425 mm long, 150 mm diameter polyhloride tube, and filled with 12.4 kg of sieved, fine-textu

li

o-

es-

rser

a

l

he irrigation was stopped. As Narayen began podding 1ater than the other cultivars, irrigation was maintained u00, 107 and 114 DAS for ES, MS and LS, respectively,

hen the irrigation was stopped. For each genotype, 28ere used, seven per treatment; four pots for the meaent of pod production, abortion and seed yield, and tere used for the measurement of leaf water potential aampling of leaves for leaf water potential can affect leafnd branch development. Three pots in the control treatere also used for the measurement of early pod androwth. The 112 pots were randomized on benches ineplicate blocks and the benches moved within the greenheekly to minimise any variation in light and temperature onlants.

.3. Podding date

For each plant in each treatment and cultivar, the start anf podding was recorded. Every second day from the beginntil the end of pod set, each new visible pod (about 2 mm ln the plants used for the pod production studies was tagge

ts podding date recorded. Similarly, the new pods on theell-watered control plants for the measurement of earlynd seed growth were tagged in Tyson, Sona and Kaniva frst 15 days and in Narayen for the first 19 days after poDAPS).

.4. Leaf water potential

Using the pressure chamber technique as describediously (Leport et al., 1998) and following the precaution

238 L. Leport et al. / Europ. J. Agronomy 24 (2006) 236–246

described byTurner (1988), the leaf water potential (Ψ l ) ofupper (unshaded) fully expanded leaves was measured aroundmidday (1030–1430 h) on clear sunny days (photosyntheticallyactive radiation above 1700�mol m−2 s−1) at 3- to 4-day inter-vals from when water was withheld to 23 days after irrigationwas terminated. The measurements were performed on mainstem or lateral branches (no differences were observed whendirect comparisons were made) for each cultivar and treatmenton the three pots not used for pod production and abortion mea-surements.

2.5. Pod and seed growth

For the early pod and seed growth study, all the pods were har-vested at 15 DAPS for Tyson, Sona and Kaniva and at 19 DAPSfor Narayen and dried to constant weight in a forced-draughtoven at 70◦C. For each cultivar, all pods with same date of podset were combined and partitioned into pod walls and seeds forcounting and weighing.

2.6. Pod production, abortion and dry matter partitioning

When the plants reached maturity, they were harvested atsoil level and individually partitioned into primary and sec-ondary branches. Primary branches were defined as the largeststems growing near the base, which included the mainstema s ot 3–9 sonS ands eighi tol edt ve-g ands seedd

herea r nos oneo she( rtilep boti bor-t podc avea ortes

2

eacc entsd latef ove-g odsp r po

the seed weight per plant and the average seed size (weight) werecalculated.

2.8. Statistical analysis

The data were analysed as a randomized complete blockdesign using Genstat 6.1 (©Lawes Agricultural Trust, Rotham-sted Experimental Station, 2003). Where means and standarderrors are presented, they were calculated with Microsoft Excel2000 (©Micrsosoft Corp., 1985). Regressions were fitted usingSigmaPlot 8.0 (©SPSS Inc., 2002).

3. Results

3.1. Phenology, and pod and seed development

Pod set commenced 10 days after flowering at 82, 85, 87 and98 DAS for Sona, Kaniva, Tyson and Narayen, respectively. Inthe well-watered plants (controls), podding ended 114 DAS inSona and Kaniva, 117 DAS in Tyson and 126 DAS in Narayen.The plants in the ES, MS, and LS treatments finished podding11, 9 and 2 days earlier on average than in the respective well-watered controls.

The growth of the pod wall, as measured by dry weight,occurred earlier than the seed (data not presented). Pod wall dryweight followed a sigmoid growth pattern and reached a maxi-m ona,a andN id notdwT cu-m PSw notp

od,s e first-f f theb types,e thep d perp thec own).P ssiona es ins y ands

teredp er asi b-u zedd ndN ed to 5at lti-v n(

nd the branches growing from the lowest three nodehe mainstem. The secondary branches grew from nodes–12, 12–15 and 7–10 of the primary branches in Tyona, Kaniva and Narayen, respectively. Each primaryecondary branch was dried separately to constant wn a forced-draught oven at 70◦C and then partitioned ineaves, stems, and individual pods. Leaflets that had shhe time of harvest were not included in the total aboround biomass. Each pod was partitioned into pod walleeds. All the samples were weighed and the number ofetermined.

The tagged pods were put into four categories: (i) tags wpod was no longer present, (ii) small pods with small o

eed, (iii) large pods with no seed, and (iv) large pods withr more seeds. While (i) represents the pods that wereii) and (iii) represent infertile pods, and (iv) represent feods. For the purposes of this paper, pod abortion refers to

nfertile and shed pods (the sum of (i)–(iii)), while seed aion refers to the reduction in the number of seeds within aontaining more than one seed. Seeds less than 40% of thege size for any one genotype were considered to be abeed.

.7. Seed yield and yield components

Seed yield and yield components were determined forultivar and treatment from the dry weight measuremescribed above. The harvest index at maturity was calcu

rom the ratio of seed dry weight (non-aborted) to total abround plant dry weight. The number of fertile and infertile per plant, the number of non-aborted seeds per plant and pe

f5,,

t

at

s

d,

h

r-d

h

d

d,

um at 9–13 DAPS in the two desi cultivars, Tyson and Snd about 17–19 DAPS in the two kabuli cultivars, Kanivaarayen (data not presented). Early mean seed dry weight differ among genotypes and was only 0.012± 0.001 g at 9 DAPShen the mean pod wall weights varied from 0.035± 0.002 g inyson to 0.094± 0.005 g in Kaniva. Rapid seed dry weight aculation did not commence in all four cultivars until 13 DAhen the pod walls were near their final dry weight (dataresented).

At maturity, the pod wall weight per pod, seed weight per peeds per pod and seed size decreased acropetally from thormed basal pods to the later-formed pods near the tip oranches in each of the adequately watered chickpea genoxcept in Kaniva in which the number of seeds per pod onrimary branches was not significantly greater than 1 seeod (Fig. 1a and b). A similar decrease was observed inhickpeas subjected to the stress treatments (data not shrovided the pods were initiated on the same day, regrenalysis showed that there were no significant differenceed and pod characteristics among pods on the primarecondary branches (Fig. 1a and b).

The average seed size (weight/seed) in the well-walants at maturity varied across cultivars in the same ord

n the seeds used at sowing (Fig. 2). The small-seeded kali cultivar, Narayen, was similar in size to the medium-siesi cultivar (Fig. 2b and d). In the kabuli cultivars, Kaniva aarayen, about 35–40% of the pods had no seeds comparnd 15% in Tyson and Sona, respectively (Fig. 2e). Although

he individual seed sizes varied markedly in all four cuars, the majority of the seeds were within±50% of the meaFig. 2e).


3.2. Development of water deficits

During podding, the midday leaf water potential in thewell-watered plants on clear sunny days was about−1.0 MPain all four cultivars (Table 1). As the plants were grow-ing rapidly at the time of the imposition of the water stresstreatments, the rate of development of the water deficit wasslower in the ES treatment as the plants were smaller thanin the MS and LS treatments when the plants were larger(Table 1). With the imposition of the ES treatment, the mid-day leaf water potential decreased at 0.17 MPa day−1 from3 to 4 days after the stress was imposed in the two desicultivars compared to a decrease of 0.19–0.28 MPa day−1 inthe two kabuli cultivars (Table 1). In the MS and LS treat-ments, the midday leaf water potential began to decrease2–5 days after the imposition of the stress treatment anddecreased at a rate of 0.4–0.5 MPa day−1 in all four cultivars(Table 1).

3.3. Effect of terminal stress on biomass, seed yield and itscomponents

The total above-ground biomass and seed yield produced bythe four genotypes in the well-watered controls by maturity wassimilar at 42–48 and 20–24 g plant−1, respectively (Fig. 3a andb). For each treatment and genotype, there was an average offour primary branches per plant. The primary branches (withouttheir leaves) represented an average of 30% of the above-groundvegetative dry matter, while the secondary branches representedan average of 8% of the above-ground vegetative dry matter.When subjected to water stress, both total biomass and seed yielddecreased to a greater extent the earlier the stress was imposed.However, the seed yield decreased more than the biomass withthe stress treatments, so that the harvest index also decreasedlinearly with the duration of water stress in all four genotypes(Fig. 3e). The harvest index was lower in the well-wateredNarayen than the other cultivars, while the two kabuli cultivars,

F(os

ig. 1. (a) The seed weight per pod (�, ©), pod wall weight per pod (�, �) and (bclosed symbols) and secondary (open symbols) branches at different dates af the branches) in four chickpea genotypes in the well-watered control treatecondary (dashed line) branches.

) seed number per pod (�, �) and seed size (�, ♦) for pods set on the primaryfter first pod set (from the first-formed basal pods to the later-formed pods near the tipment. The lines are the fitted linear regressions for the primary (unbroken line) and


Fig. 1. (Continued ).

Kaniva and Narayen, were more severely affected by the longerperiods of stress than the desi cultivars, so that in the ES treat-ment the seed yield and harvest index in the two kabuli cultivarswere significantly lower than in the two desi cultivars (Fig. 3band e).

All cultivars had more than one seed per pod on average. Inthe well-watered plants, the number of pods with more thanone seed was 4% in Kaniva, 21% in Narayen and 37% inthe two desi cultivars (Fig. 3c). The stress treatments did notsignificantly affect the number of seeds per pod in the twodesi cultivars, but the ES treatment reduced the seed num-ber to a single seed per pod in the two kabuli chickpeas. Thestress treatments had a much smaller effect on seed size (28%reduction in the ES treatment on average) than on seed yield(90% reduction in ES treatment on average). Although seedsize was not reduced by the LS treatment, the mean seed sizewas significantly reduced in the ES treatment in all cultivars(Fig. 3d).

3.4. Effects of terminal stress on seed production by theprimary and secondary branches

In the well-watered plants, pods set on the same date hadthe same seed characteristics whether the seed was produced onthe primary or secondary branches (Fig. 1). However, stress hada major impact on the productivity of the secondary branches.In Tyson, the imposition of the terminal stress at the beginningof podding (ES) reduced the number of pods on the secondarybranches by 89% compared to a reduction of only 38% on theprimary branches, and reduced the seed yield of the secondarybranches by 99% compared to 66% in the primary branches(Table 2). In the other cultivars the ES treatment had also agreater effect on the secondary compared to primary branches.However in Sona, seed abortion on the secondary branches wasless and the seed yield was reduced less by the ES treatment thanin the other three cultivars (Table 2). In addition while there wasa decrease in average seed size on the secondary branches in


Fig. 2. The frequency distribution of the number of seeds per plant (a–d) and proportion of seeds (e) as a proportion of the average seed size in four genotypes ofchickpea, (a) Tyson, (b) Sona, (c) Kaniva and (d) Narayen in the well-watered control treatment. The average seed size for each genotype is given.

all of the genotypes, the differences among the cultivars in seedsize observed on the primary branches were not observed in theseeds on the secondary branches (Table 2).

3.5. Pod development under stress

The stress treatments affected both the production and abor-tion of pods. The ES treatment had the major effect on thenumber of pods at maturity in all genotypes (Fig. 4). Compared

to the well-watered controls, the total number of pods per plantin the ES treatment was reduced by 66–75%. The later stresstreatments, particularly the LS treatment, had less of an effecton pod production (Fig. 4). Fig. 4also shows that after the stresstreatments were imposed pod numbers began to decrease belowthose in the well-watered plants about 5 days after the impositionof the stress. This coincides with the time that the midday leafwater potential first began to decrease below that in the controlsin all the stress treatments and genotypes (Table 1).


Table 1The time to the start and the rate of decrease of leaf water potential (Ψ l ) afterwater was withheld in the three stress treatments (early, middle and late termi-nation of watering) and four chickpea genotypes

Stress Time to start (days afterwater withheld)

Rate of decrease inΨ l (MPa day−1)

Tyson (−1.01 MPa)Early 3.3 0.17Middle 3.9 0.45Late 4.6 0.39

Sona (−1.02 MPa)Early 4.2 0.17Middle 2.1 0.46Late 3.6 0.45

Kaniva (−1.03 MPa)Early 2.9 0.28Middle 1.9 0.48Late 3.9 0.43

Narayen (−0.94 MPa)Early 4.3 0.19Middle 3.4 0.45Late 4.1 0.50

The mean value of the leaf water potential in the control plants of the fourcultivars is given in parenthesis.

Even in the well-watered chickpeas, 10–23% of the pods onthe primary branches were aborted (Table 3). On the secondarybranches the abortion was greater, particularly in the two kabulicultivars, Narayen and Kaniva, even in the well-watered plants.The imposition of water stress increased pod abortion to between28 and 48% on the primary branches and between 55 and 82%on the secondary branches in the desi cultivars (Table 3). Podabortion was significantly greater (P < 0.001) in the two kabulicultivars than the two desi cultivars independent of seed size andwas significantly greater (P < 0.001) in all three stress treatmentsthan in the well-watered controls (Table 3).

4. Discussion

Chickpea is an indeterminate annual cool-season grainlegume that produces its seeds progressively (acropetally)along the branches. In water-limited Mediterranean and sub-tropical environments, the plants are usually subjected to ter-minal drought unless irrigated. In a greenhouse experiment,Behboudian et al. (2001)showed that a water deficit imposed

Table 3The percentage of the total pod number that had aborted at maturity on theprimary and secondary branches in four chickpea genotypes given four stresstreatments: well-watered control, early (ES), middle (MS) and late (LS) termi-nation of irrigation

Pod abortion (% of total pod number)

Control ES MS LS

PrimaryTyson 10.5 27.6 29.8 33.7Sona 14.6 41.3 48.3 42.5Kaniva 23.0 64.0 66.1 47.2Narayen 17.7 71.0 56.0 59.5

SecondaryTyson 12.3 82.5 71.2 54.6Sona 17.3 53.1 70.7 58.5Kaniva 39.2 99.0 92.4 74.5Narayen 26.4 86.2 79.6 79.3

LSD (P < 0.05) = 13.6.

from the beginning of podding reduced pod numbers in the culti-var Sona by reducing both the production of pods and increasingpod abortion. The present study has shown that the timing of theimposition of terminal drought has a major impact on both theproduction and abortion of pods and hence on seed yield, andthat the response varies depending on whether the chickpea is adesi or kabuli type. Moreover, seed size per se does not appearto have an influence on pod production or abortion.

Previous field studies have shown that in a Mediterranean-type environment water deficits develop near the onset of pod-ding (Leport et al., 1998, 1999), induce faster and shorter seedfilling (Davies et al., 1999), reduce pod and seed number, andreduce seed yield and seed size (Davies et al., 1999; Leport etal., 1999). Under terminal drought conditions, kabuli types ofchickpea have a greater reduction in yield and pod numbers perplant compared to desi types (Leport et al., 1999; Siddique etal., 1999). This may be associated with their later flowering andpodding than the desi types (Leport et al., 1999) and thereforegreater vulnerability to decreasing soil moisture. However, in thepresent study, the water deficits were imposed at the same timeafter first pod set in both types of chickpea and the kabuli typesstill had greater reductions in yield and pod number than thetwo desi types when the stress was imposed from early podding.On average, terminal water stress increased pod abortion 50%in the desi cultivars and 75% in the kabuli cultivars. This com-

Table 2The seed yield and pod number per plant as a percentage of the well-watere ary (first) ansecondary (second) branches in four chickpea genotypes in the early stress tr

Seed yield (% of control) Pods plant−1 (% of c

econd

T 0.7S 4.6K .5N 2.7

L

First Second First S

yson 34.1 1.1 61.9 1ona 27.2 10.5 45.6 2aniva 10.3 0.3 39.0 27arayen 4.5 2.9 30.0 2

SD (P < 0.05) 5.4 6.6 12.5 ns

d controls and the seed number per pod and average seed size of primdeatment

ontrol) Seeds pod−1 Average seed size (g)

First Second First Second

1.51 1.00 0.093 0.0721.67 1.43 0.135 0.1201.00 1.00 0.244 0.1011.00 1.00 0.113 0.096

0.25 0.33 0.80 ns


Fig. 3. The relationship between (a) total above-ground biomass (excluding shed leaves) per plant, (b) seed yield per plant, (c) seed number per pod, (d) seed size,and (e) harvest index, and the time that the plants were without irrigation in four chickpea genotypes, Tyson (�), Sona (�), Kaniva (�) and Narayen (�). Values aremeans± one standard error of the mean (n = 4).

pares with 35% of pods being aborted in a desi genotype in thefield at a low rainfall site that received on average about 210 mmof growing-season rainfall (Siddique and Sedgley, 1986). In thepresent controlled-environment study, higher rates of pod abor-tion as a result of water stress were expected because the initialnumber of pods set in the greenhouse was not reduced by thelow temperatures that hinder pod set in the field (Croser et al.,2003). Moreover, the rate of development of the water stress wasmore rapid in the greenhouse than in the field, even though theminimum leaf water potential (−3.0 MPa) in both environments

was similar (Leport et al., 1998). However, what was of notein the present study was the much greater effect of the waterdeficits on pod abortion on the secondary branches comparedto the primary branches, particularly in the two kabuli cultivarsin which pod abortion on the secondary branches was between74 and 99%. While the final seed and pod characteristics of thesurviving pods on the primary and secondary branches set onthe same day were similar (Fig. 1), the delay in pod set on thesecondary branches clearly had a big influence on the survival ofthose pods under terminal drought. This suggests that the devel-


Fig. 4. Cumulative pod number after first pod set in four genotypes of chickpea given four water stress treatments: C, well-watered control; ES, early stress; MS,middle stress; and LS, late stress. The arrows denote the time that the stress treatments were imposed. The mean± one standard error of the mean (n = 4) is given forthe final pod numbers only.

opment of early flowering kabuli genotypes may not give thesame benefit to yield as the development of early desi genotypesfor water-limited environments (Berger et al., 2004), unless theinitiation and development of pods on the secondary branchescan also be enhanced. Moreover, it suggests that if supplemen-tary irrigation is available, this should be used as a preferenceon kabuli chickpea which are more susceptible to water deficitsand respond better to supplemental irrigation than desi types andthat irrigation at flowering and early podding when chickpeais most sensitive to water deficits (Khanna-Chopra and Sinha,1987) will be much more beneficial than irrigation later in poddevelopment.

Seed size per se does not appear to be a major factor affectingpod abortion. Pod abortion was high in both kabuli types thatdiffered in seed size, but much lower in Sona than in Narayen,despite their similarity in seed size. At the time that the middaywater potential began to decrease below that in the well-wateredcontrols, seed development was minimal and seed size was sim-ilar in all four cultivars and there was no difference in pod-wall

dry weight between Sona and Narayen. Thus, the rate of growthof the pod or seed during early seed growth was not consid-ered to be a factor that affected the different degrees of podabortion. The desi cultivar Sona was selected for its high yield,and early and high pod production in Mediterranean-type envi-ronments (Siddique and Khan, 2000). The present study hasshown that with terminal water stress this cultivar had lowerpod and seed abortion and better maintenance of seed sizeon the secondary branches than the kabuli cultivars, suggest-ing that selection for earlier pod set, particularly on secondarybranches, can lead to higher yields under terminal drought. Thedesi gene pool is considered older, and hence closer to the wildprogenitor,Cicer reticulatum, than the kabuli chickpea that isregarded as a more recent evolutionary branch of the cultigen(Ladizinsky, 1995). Thus, it is likely that genetic variation forat least some characters is narrower in the more-recent kabulitypes than in the desi types (Abbo et al., 2003). Our observationsare consistent with those ofLiu et al. (2003)who compared thepod abortion of kabuli and desi chickpea subjected to crowd-


ing and concluded that kabuli types of chickpea are inferior todesi types in their morphological plasticity. Therefore, we sug-gest that, irrespective of seed size, there was a greater abortionof pods by the kabuli than desi cultivars in response to watershortage as a result of the more-recent evolutionary history andsmaller selection pressure for drought resistance among kabulitypes.

The development of stress in the four cultivars was verysimilar (Table 1). In all cases the reduction of pod productionoccurred at the same time as the decrease in midday water poten-tial was first detected and well before the leaf water potential waslikely to have reduced the rate of leaf photosynthesis (Leport etal., 1999; Ma et al., 2001). Previous studies have shown thatthe pod water potential is higher than the leaf water potential(Leport et al., 1999) and that the turgor pressure of the seed coatis unaffected by a decrease in the water potential of the podsand leaves (Shackel and Turner, 2000). This suggests that thegrowth of the pod and seed was not reduced as a consequenceof the water potential or turgor pressure of those organs, norfrom a lack of assimilates, but that pod and seed production andabortion was possibly affected by root signals (Emery et al.,1998).

As chickpea is indeterminate, the branches continue todevelop, flower and set pods and seeds while water is avail-able and temperatures are neither too cold (Croser et al., 2003)nor too hot. This study has shown that the seed dry weight, seedsp aredt of tht prod doen simil tes ft eastw et tself( ns nt fov

5

erem kpec iffer-e n inb ondt daryb enca e oft poseo bult t pow onc heres ivent d ah

Acknowledgements

We thank Mike Barr, Rebecca Carpenter and Christiane Lud-wig for assistance with the measurements of dry weight anddata processing. We also thank Drs. Patrizia Gremigni, JairoPalta, Jens Berger, Shahal Abbo and Peter Hocking for theircomments on the manuscript. This research was supported byCSIRO, the Centre for Legumes in Mediterranean Agricultureat the University of Western Australia, and the Grains Researchand Development Corporation of Australia.

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C M.C.,eas., pp.

D L.,

c. 39,

E 998.their

F cling

K cts ofpea.

K ctionsen,ick-earchbpur,

L Evo-

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L ical26–

M ange

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. Conclusions

This study has shown that the kabuli chickpea cultivars wore susceptible to terminal water stress than desi chic

ultivars and that this was not related to seed size or dnces in phenology. Further while there was a reductiooth total biomass and pod production under the stress c

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toe-s

-orin

r

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i-

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variation in pod production and abortion among chickpea cultivars under terminal drought

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