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Breeding for increasing wheat yield in the cold dryland regions of Iran

Siroos Mahfoozi1 , Mozaffar Roustaii2, Shahryar Jasemi 1 , Habib Ketata3 and David B. Fowler

1SPII, Seed and Plant Improvement Institute, P.O. Box No 31585-4119., Karaj, Iran Email siroosmahfoozi@yahoo.com
3
DARI, Draland Agricultural Research Institute, P.O.Box No., 119, Maragheh, Iran
3
ICARDA, International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria,
E-mail h.ketata@cgiar.org
4
Department of Plant Sciences at the University of Saskatchewan, Canada, Email Brian.Fowler@usask.ca

Abstract

The objective of this study was to determine: 1) ) genetic variation in local and modern winter wheat gene pool for rate and duration of kernel filling, 2) if position in the spikelet and position along the spike were important restrictions to cultivar grain yield potential in the dry land areas of Iran. All genotypes had significant differences in the number and the weight of kernels in the A, B (basal), C and D (distal) positions in the spikelet with fewer and lighter kernels in the C and D kernels of spiklets. However, the weight of kernels in the A and B position in the spiklets were heavier in both local and modern genotypes. Kernel numbers and weights were varied along the length of the spike with kernels from the lower and middle part of the spike significantly heavier than those from the upper part. Among the genoypes examined, the higher rate of kernel filling and greater kernel weights were achieved in widely grown local ‘Sardari’ and in new lines derived from Sardari, although more sites and years are needed to provide a breeding guide lines for improvement of grain yield in cold dry land areas. Considerable variation for a higher rate of kernel filling, kernel weight and yield composition exists for increasing yield in the gene pool of Iranian National Plant Gene Bank. Selection of cultivars with higher rate of kernel filling and large kernel size may increase wheat production in the dry areas of Iran.

Media summary

Variation for higher kernel filling rate, kernel weight and yield composition exists for increasing yield in the gene pool of Iranian Wheat Gene Bank.

Key words

Triticum aestivum L., grain potential, grain filling, yield components

Introduction

Higher rate of kernel filling is characteristic of most Iranian wheat cultivars widely grown in the dry areas prone to terminal drrought stress in Iran. Genetic variation for kernel growth has been recorded by many researchers in modern wheat cultivars (Darroch and Baker, 1990; Hunt et al, 1991; Darroch and Baker, 1995), however, the growth pattern and genetic variation in both the rate and duration of kernel growth is poorly understood and little is known about when kernel growth phases are achieved particularly in Iranian modern and local wheat cultivars grown in cold dry land regions prone to terminal drought stress.

Large kernel size and fewer kernels in spikes are characteristics of most Iranian wheat genotypes in the dry land areas of Iran. Wheat spikelets contain basal and distal kernels. Distal kernels are smaller and lighter than the basal kernels in the spikelet. Increased contribution to yield by the more distal kernels in the spikelet has increased the grain yield potential of modern cultivars in the world (Miralles and Slafer, 1995). Increasing the number of spikelets per spike is another possible way of increasing grain yield (Siddique et al, 1989).

Understanding the genetic variation among genotypes may help to increase grain yield in dry areas. The objective of this study was to determine: 1) ) genetic variation in local and modern winter wheat gene pool for rate of kernel filling in cold dry land region with terminal drought stress, 2) if position in the spikelet, position along the spike and rate of kernel filling were important restrictions to cultivar grain yield potential in cold dry land areas of Iran.

Materials

Two local (914Gene Bank and Sardari) and four modern winter and facultative wheat genotypes (8484Mashad/Sabalan; 96YRRGP; Fengkang15/Sardari; Kvz/Tm71/3/Maya “s”//Bb/Inia /4/Sardari and Azar-2) were grown on rainfed conditions at Maragheh agricultural research station ((37o15’N, 46o15’E; 1720m) in the cold dry land region of Iran in 2002/3. The experimenal design was a randomized complete block with three replications. Plot size was 1.2 m X 5 m and row spacing was 20 cm and were seeded at the rate of 350 seeds/m-2. For seed germination and plant establishment, all genotypes were irrigated once at planting time in October 2002. Five spikes were removed from each plot every second day from beginnig of anthesis to physiological maturity to determine the kernel growth pattern. Spikes were dried at 60C for 48 h in chambers and threshed. Kernels were weighed, counted and average kernel weights determined. In order to determine the contribution of basal and distal kernels in grain yield of modern and local cultivars, ten spikes from each treatment were harvested and dried at maturity. Kernels were then hand-sorted into A, B, C and D kernel position in the spikelet, counted and weighed. Ten spikes from each treatment were also harvested and dried at maturity to determine the genetic variation of kernel number and weight along the spike length. Spikes were then divided into upper, middle and lower third sections based on the number of spikelets spike-1. Segments were then hand threshed, the number of kernels determined and weighed.

Results

The season was characterized with a higher rainfall and relatively a mild spring with good rainfall distribution. All genotypes performed well under rainfed conditions. Significant differences in yield were observed among genotypes in both local and new wheat genotypes. Basic trends in kernel growth of all genotypes were similar with a characteristic ‘lag’ phase, followed by an exponential growth phase and finally plateauing to maximum dry weight (Fig 1). Overall rates of various phases differed significantly between genotypes (Table 1). Sardari (genotype no.6) which is a widely grown old winter local wheat cultivar in the cold dry land areas of Iran had an increased rate of kernel filling compared to other genotypes. Sardari tended to display greater rates of kernel filling during the exponential growth phase, and attained its maximum kernel weight in fewer days after anthesis (Fig 1). A local wheat genotype from National Gene Bank (no.1) and genotypes derived from Sardari cultivar achieved their maximum kernel weight relatively sooner than the other modern genotypes.

Genotypes differed significantly in the number and weight for each kernel position (Table 1). For all genotypes the majority of the grain yield originated from kernels originating in the A and B kernel positions. Kernel weights from the upper third of the spike were consistently less that those from the middle and lower thirds of the spike (Table 2). Grain from the upper third of the spike contributed significantly less to grain yield than the middle and lower thirds of the spike for all genotypes used in this experiment.

Fig.1. Kernel development on the basis of number of days after anthesis to physiological maturity in seven winter and facultative wheat genotypes grown under rainfed conditions at Maragheh agricultural research station in the cold dry land region of Iran in 2002/3 (gray line is Sardari.local check)

Table 1.Rate of kernel filling,grain yield and number and weight of basal and distal kernels in contriution to grain yeild of seven local and modern winter and facultative wheat genotypes from various kernel positions in 2002/3

Genotype

Rate of
Kernel filling
(mg/d)

Yield
Kg/ha

No of
Kernels A/spike

W (g) of
Kernels A/spike

No (g) of
Kernels
B/spike

W (g) of
Kernels B/spike

No of
Kernels
C/spike

W (g) of
Kernels
C/spike

No of
Kernels
D/spike

W(g) of Kernels
D/spike

1

2.02cd

2801a

9.9abc

0.05a

9.63ab

0.05a

0.1b

0.01b

0.033b

0.01b

2

1.817de

2481a

11.8a

0.04a

11.20a

0.04a

1.2ab

0.03a

.0.083ab

0.031b

3

1.568e

1657b

9.4bc

0.04a

9.9ab

0.038a

0.76ab

0.03a

0.5ab

0.11a

4

1.96cd

2733a

10.4abc

0.044a

10.13ab

0.043a

1.33ab

0.03a

1.0ab

0.032b

5

2.497ab

1596b

8.5c

0.053a

8.3b

0.052a

1.167ab

0.04a

1.33a

0.037b

6

2.629a

2482a

10.4abc

0.047a

9.97ab

0.048a

0.866acb

0.02ab

1.03ab

0.022b

7

1.81de

2755a

11.67a

0.045a

11.43a

0.045a

1.9a

0.05a

1.3a

0.035b

LSD(P=0.05)

0.30

306

1.85

0.02

1.8

0.02

1.43

0.02

1.12

0.08

Means with the same letters are not significantly different

(Genotype 1=914Gene Bank material (local); 2=8484Mashad/Sabalan (new line); 3= 96YRRGP (new line); 4= Fengkang15/Sardari (New line); 5=Kvz/Tm71/3/Maya “s”//Bb/Inia /4/Sardari (new line); 6=Sardari (old local); 7= Azar-2 (new cultivar)

Table 2. Average weight and number of kernels from the lower, middle and upper sections of the main spike for seven winter and facultative local and modern wheat genotypes grown in the cold dry land region of Iran

Genotype

I

II

III

IV

V

VI

Spk/S

K/S

1

5.9cd

0.267b

5.8e

0.268c

4c

0.16c

11.6ab

17.8c

2

11a

0.494a

10.53a

0.49a

7.07a

0.29a

13.27a

30.6a

3

7.3bcd67

0.34b

7.97abcde

0.37abc

6.13ab

0.25ab

11.63ab

20.8bc

4

5.967cd

0.32b

6.03de

0.34bc

4.8bc

0.24abc

9.33c

26.6a

5

5.4d

0.25b

5.87e

0.28c

4.13c

0.17c

11.47ab

19c

6

7.533bcd

0.33b

8.6abcd

0.39abc

6.47ab

0.26ab

12.47ab

21.33bc

7

8.29bc

0.32b

8.88abc

0.37abc

6.66a

0.27ab

11bc

24.67abc

LSD (P=0.05)

2.36

0.10

2.46

0.13

1.64

0.074

1.75

6.6

Means with the same letters are not significantly different

I, III and V=Number of kernels in lower, middle and upper section of spike, respectively.
II, IV and VI=Weight of kernels in lower, middle and upper sections of spikes, respectively. Sp/S= No of spikelets/spike; K/S=No of kernels/spike
Genotypes (1,2,3,4,5,6,and 7) are the same as in table 1.

Current winter wheat genotypes vary considerably in the rate and duration of kernel filling. Significant variation also exists for how kernel weight and kernel numbers vary between the various kernel positions along spike and spikelets. It is suggested that considerable improvements in grain yield of winter wheat can be made through increased rate of kernel filling in the dry land areas prone to terminal drought stress. Further studies in different years and sites (with low and high drought stress levels) are required to understand the genetic variation in kernel development and to know how yield should distribute among basal and distal kernels in cultivars grown in the dry land areas.

References

Darroch, B.A. and R.J., Baker 1990. Grain filling in three spring wheat genotypes: Statistical analysis. Crop Science. 30:525-529.

Darroch, B.A. and R. J. Baker 1995. Two measures of grain filling in spring wheat. Crop Science. 35:164-168.

Hunt, L.A., G. van der Poorten and S. Pararajasingham 1991. Postanthesis temperature effects on duration and rate of grain filling in some winter and spring wheats. Canadian Journal of Plant Science. 71:609-617.

Miralles, D. J. and G.A. Slafer 1995. Yield, biomass and yield components in dwarf, semi-dwarf and tall isotonic lines of spring wheat under recommended and late sowing dates. Plant Breeding. 114: 392-396.

Siddique, K.H.M., E.J.M. Kirby and M.W. Perry 1989. Ear-to-stem ratio in old and modern wheats; relationship with improvement in number of grains per ear and yield. Field Crops Research. 21:59-78.

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