Differential responses of BA injection on yield and specific grain growth incontrasting genotypes of wheat (Triticum aestivum L.)

N.K. Gupta1,*, Sunita Gupta1, D.S. Shukla2 and P.S. Deshmukh2

1Department of Plant Physiology, SKN College of Agriculture, Rajasthan Agricultural University, Jobner,303 329, India; 2Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi, 110012,India; *Author for correspondence (e-mail: narendra_sunita@hotmail.com; phone: +91-1425-254038; fax:+91-1425-254022)

Received 29 January 2002; accepted in revised form 26 February 2003

Key words: Benzyladenine, Cytokinin, Grain growth, Temperature, Wheat, Yield

Abstract

The effect of exogenous cytokinin (benzyladenine) was investigated on location specific grains in three contrast-ing wheat genotypes tolerant or susceptible to post anthesis high temperature conditions. Seeds were sown inearthen pots under natural environment in November and January for normal and late sowings, respectively. Grainweight was increased by the application of benzyladenine at anthesis under late sown stress only in those geno-types, which are known, to posses temperature tolerance in developing grains. However, under normal sowingconditions BA application was effective irrespective of genotype response to late sown stress. The effect wasmost visible in distal spikelets in the spike and distal grains in the spikelet which resulted in higher increment inweight of younger grains (c and d) as compared to older grains (a and b). It has been suggested that the respon-siveness of the genotype to BA application under late sown stress is important and may be developed as anindicator to screen wheat genotypes for relative tolerance to late sown stress under irrigated conditions.

Introduction

The capacity of wheat grain to grow and accumulatedry matter depends upon the interaction of growthregulators like cytokinin and auxin while terminationof grain growth is induced by growth inhibitors likeabscisic acid (Gabali et al. 1986). The cytokinin/ab-scisic acid balance is important in imparting toleranceto heat stress (Cheikh and Jones 1994). ABA pro-duced under heat stress results in reduced endospermcell division, starch accumulation and grain abortionwhereas increased level of cytokinin during grain de-velopment either enhance cellular activity leading tothe production of a large number of endosperm cellsor help in the increased mobilization of assimilates(Ray and Chaudhary 1981; Herzog 1982). Undoubt-edly, the grain-sink potential is genetically deter-mined, the capacity of grain to develop is also a mat-ter of competition for assimilates and space createdby number of endosperm cells produced which are

largely dependent upon the ambient thermal environ-ment. Wheat genotypes possessing larger grains havebeen found richer in cytokinin like substances andgrowth of these grains was further increased by exo-genous application of cytokinin (Dua and Bhardwaj1979). Warrier et al. (1987) suggested that applicationof benzyladenine at anthesis increased the grainweight in wheat significantly possibly by increasingthe synthesis of membrane structural component aswell as attracting more assimilates towards the devel-oping grain. A positive correlation between the levelof cytokinin to grain development and final grainweight has also been reported in maize (Dietrich etal. 1995). With this background, it was felt worth-while to study whether exogenous cytokinin (benzy-ladenine) could provide tolerance to location specificgrains of wheat genotypes recommended for normaland late sown conditions.

201Plant Growth Regulation 40: 201–205, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

Material and methods

Three wheat genotypes were studied, viz. Kalyanso-na- a genotype with a wider adaptability and hightemperature tolerance in developing grains, HD 2285-recommended for late sowing and HD 2329-recom-mended for normal sowing. Seeds of these genotypeswere raised in 300 pots (20 cm height and 30 cm di-ameter) filled with 12 kg of air dried, well sieved soilmixed with one eighth part by volume of fully de-composed farmyard manure. 2 g urea, 2 g single su-per phosphate and 1 g muriate of potash were addedto each pot and mixed well with the soil before sow-ing. One hundred well prepared pots were used foreach genotype. Sowings were done on 15 Novemberand 10 January of two consecutive years for normaland late sowings, respectively.

After thinning, four uniform seedlings at equalspacing were maintained in each pot. A split dose of2 g urea per pot was added again 35 d after sowing.Irrigation was provided as and when required. Mothershoots (MS) in all the pots were tagged and the dateof anthesis was recorded carefully. The day by which75 per cent of the mother shoots of all the pots of agenotypes came to anthesis was taken as the meanvalue of anthesis for that genotype.

Freshly prepared benzyladenine (BA) solution wasinjected at the base of the mother shoot at anthesis.20 µl of BA solution containing 2 µg of active ingre-dient was injected into each plant with a micro sy-ringe through the needle holes already made in theinternode just below the peduncle. Control plantswere injected with 20 µl of distilled water.

Plants were harvested at maturity and data on grainnumber, grain weight, grain and biological yield wererecorded for mother shoot (MS) and tiller ears (TE)separately. Harvest index was calculated by the for-mula of Singh and Stoskoff (1971): Harvest Index(%) = (Economic yield / Biological yield) × 100. Forgrain location studies, the spikelets of MS ears wereseparated into top (spikelet number 14–22 from base),middle (spikelet number 10–13 from base), and bot-tom (spikelet number 3–9 from base) regions. Thegrains were categorised according to their position inthe spikelet. The basalmost grain was designated asgrain ‘a’ while subsequent grains were termed as ‘b,c, and d’, depending on their location from base toapex. Statistical analysis was done for yield attributesand each grain position of top, middle and bottomspikelets using a completely randomized block de-sign. Critical differences at P = 0.05P are given only

for those treatments where significant differences ex-ist.

Results and discussion

A general reduction in grain yield of all the genotypesunder late sown conditions has been recorded, due toshortened vegetative and reproductive phases. Reduc-tion in phenophases of wheat under later sowings andconsequent decline in yield has been well docu-mented in the literature (Warrier et al. 1987; Samuelet al. 2000; Gupta et al. 2002). BA application in-creased the yield in most of the treatments, but theresponse was variable. Under normal sowing condi-tions maximum increase was exhibited in HD 2329(13.30%) whereas under late sowing the increment inits yield was marginal (4.47%). The other genotypesresponded well under both the sowings. Exogenouslyapplied BA enhanced the grain yield of Kalyansonaand HD 2285 by 8.8 & 13.70%, 5.66 & 13.33%, un-der normal and late sown conditions, respectively(Table 1). Cytokinin induced enhancement in seedyield has also been reported in soybean (Nagel et al.2001). The grain yield of MS and TE were recordedseparately and it was observed that BA injected intothe peduncle of the mother shoot increased the yieldpotential of MS only (Table 1). These observationsstrengthen the earlier findings that cytokinin do notreadily move from the site of production/applicationto the non-treated areas in the same leaf (Borkovecand Prochazka 1992).

Examination of the number of grains per ear (MS)indicated a genotypic variation but BA application didnot enhance the number in any case (Table 1). Thismeans that the grain yield was increased only by in-creasing seed weight (1000 grain weight) in all thethree genotypes under normal as well as late sownconditions. This result is in contrast to those of Trck-ova et al. (1992) who reported that foliar applicationof cytokinin enhanced grain number and dry mass.Warrier et al. (1987) also reported that incorporationof BA into the vascular channel of wheat ear in-creased its grain yield mainly through enhancementin grain size. The increase in harvest index as a resultof BA application is also a reflection of the changesin dry matter accumulation by enhanced sink size andpartitioning of dry matter towards the grain sink (Fig-ure 1). It has been reported that exogenously appliedcytokinin increases the endosperm material by stimu-lating photosynthesis in wheat (Rabie 1996) and pho-

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tosynthesis unloading from seed coat to endosperm inmaize (Dietrich et al. 1995). Thus, our data indicatethat the external application of cytokinin enhancedthe growth and productivity of wheat genotypes un-der adverse conditions but the response was morepronounced in tolerant genotypes. Improvement inwheat yield by external application of cytokinin un-der normal sowing conditions has also been observedin our previous studies (Gupta et al. 2000).

The effect of BA on inter- and intra- spikelet grainsize spectrum was also compared to determine its ef-fect on younger and older grains separately. The data

show that BA treatment did not reflect significant ef-fect on a and b grains in all the genotypes (Table 2).A significant improvement in weight was noted in cand d grains located at any position in the ear. Theseresults indicate that grains within and between spike-lets received varied amounts of cytokinin, resulting inincreased sink potential of younger grains. Howeverthis response was genotype specific. The per cent in-crease in dry weight of c and d grains was greatest inKalyansona followed by HD 2329 under normal sow-ing and by HD 2285 under late sowing. In the case oflate sown HD 2329, no increase was observed on c

Table 1. Effect of benzyladenine on yield and yield attributes in mother shoot (MS) and tiller ears (TE) of wheat genotypes under normal andlate sown conditions.

Genotype Treatment Grain yield (g plant−1) Grain Number (per plant) Test weight (g)

MS TE MS TE MS TE

Normal

sown

Late

sown

Normal

sown

Late

sown

Normal

sown

Late

sown

Normal

sown

Late

sown

Normal

sown

Late

sown

Normal

sown

Late

sown

Kalyansona Control 2.50 1.46 14.00 8.12 70.0 44.0 45.0 36.0 35.71 33.18 33.82 31.54

BA 2.72 1.66 14.40 8.07 72.0 46.0 46.0 35.0 38.62 34.77 35.63 32.13

HD 2285 Control 2.47 1.65 14.90 9.35 59.0 45.0 42.0 40.0 41.82 37.50 40.28 36.19

BA 2.61 1.87 14.95 9.47 60.0 48.0 41.0 42.0 42.04 40.65 40.35 37.77

HD 2329 Control 2.63 1.34 15.96 6.98 60.0 40.0 43.0 33.0 43.44 33.75 41.55 30.56

BA 2.98 1.40 15.99 6.92 63.0 41.0 45.0 34.0 47.30 34.80 43.51 29.68

CD0.05P Genotype 0.12 0.11 1.09 0.93 3.77 2.16 2.98 2.41 2.47 1.67 2.20 2.37

BA 0.09 0.09 NS NS NS NS NS NS 2.02 1.18 NS NS

Interaction 0.17 0.16 NS NS NS NS NS NS 3.50 1.78 NS NS

Figure 1. Effect of benzyladenine on harvest index of wheat genotypes under normal sown (NS) and late sown (LS) conditions.

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and d locations as a result of BA application exceptin the case of d grains located on the bottom spike-lets (Table 3). These observations strengthen the as-sumption that when the younger grains located at ‘c’and ‘d’ locations did not respond to BA application,the loss in grain weight and grain yield could not becompensated under late sown stress in the susceptiblegenotype HD 2329. Warrier et al. (1987) also sug-gested that in relatively tolerant genotypes of wheatthe stem reserves were better mobilised to the devel-oping grains. This might be due to the increased de-mand of assimilate by BA induced enlarged grainsinks of these genotypes. It is also suggested that in-crease in grain size was related with a preceding in-crease in synthesis of NSELF (non starch endosperm

liquid fraction) required for enhancing grain storagecapacity to accumulate the assimilates in endosperm.

References

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Table 2. Effect of benzyladenine on weight of ‘a, b’ grain in contrasting wheat genotypes under normal and late sown conditions.

Genotype Treatment ‘a’ grain ‘b’grain

Normal sown Late sown Normal sown Late sown

Top Middle Bottom Top Middle Bottom Top Middle Bottom Top Middle Bottom

Kalyansona Control 39.33 49.28 43.77 33.16 35.10 37.11 37.49 49.19 45.16 31.60 34.26 28.21

BA 40.64 50.82 46.58 32.90 35.60 36.46 38.90 48.97 46.86 32.75 34.60 32.18

HD 2285 Control 46.11 55.85 50.18 38.00 40.68 40.15 46.83 54.00 50.00 37.60 39.18 39.60

BA 47.20 56.70 51.57 40.20 41.10 41.21 47.00 55.15 49.17 37.15 40.26 41.10

HD 2329 Control 49.32 61.90 51.95 34.91 36.63 36.84 47.96 50.66 50.94 32.16 35.80 34.00

BA 50.10 62.67 52.41 36.50 36.00 37.80 49.20 53.28 52.10 32.81 38.03 34.10

CD0.05P NS NS 2.36 1.12 NS NS 1.41 NS NS NS NS NS

Table 3. Effect of benzyladenine on weight of ‘c, d’ grain in contrasting wheat genotypes under normal and late sown conditions.

Genotype Treatment ‘c’ grain ‘d’grain

Normal sown Late sown Normal sown Late sown

Top Middle Bottom Top Middle Bottom Top Middle Bottom Top Middle Bottom

Kalyansona Control 33.63 37.73 35.20 29.90 30.37 28.37 28.17 34.85 31.09 21.90 28.47 25.87

BA 35.99 40.86 38.83 31.83 33.48 30.70 30.98 38.10 34.16 24.85 29.60 27.68

HD 2285 Control 39.42 44.23 40.04 35.33 36.56 35.73 32.26 38.60 36.59 24.31 31.85 29.56

BA 39.87 45.90 42.43 37.69 38.50 38.01 33.00 38.17 38.00 28.19 34.56 34.19

HD 2329 Control 40.74 43.20 42.56 30.49 32.15 32.14 30.77 39.72 38.16 22.67 28.60 21.85

BA 43.31 46.29 44.54 30.83 33.67 33.53 33.28 42.11 40.87 24.90 28.50 23.16

CD0.05P 1.68 1.71 1.49 1.64 1.60 1.35 1.83 1.48 1.27 1.41 1.22 1.05

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