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Screening for late season drought tolerance in wheat genotypes grown in Iran

Goodarz Najafian1, Akbar Ghandi2 and Hassan Abdi3

1Cereal Research Department, Seed and Plant Improvement Institute, Karaj, Iran. goodarzn@yahoo.co.uk
2
Agricultural Research Center, Isfahan, Iran.
3
Agricultural Research Center, Varamin, Iran.

Abstract

Considering the importance of seasonal drought and water shortages for irrigation, a trial aimed at identifying wheat varieties tolerant to terminal drought was performed. In this study 51 lines and varieties of bread wheat along with 3 check cultivars (Marvdasht, Cross of Alborz and Azar-2) were planted under late season water stress at three locations; Kermanshah, Isfahan and Varamin. These 51 entries were divided to 3 sets, which along with the above 3 checks included 20 genotypes in each group. These 3 experiments (WS1-WS3) were planted in a Randomised Complete Block (RCB) design with 4 replications. These trials depended on rainfall apart from some supplementary irrigation applied following the cessation of rainfall in May 2003. Every experiment was therefore exposed to water stress from the heading stage onward. Combined ANOVA showed significant effects for location, genotypes and GE interaction, in all 3 experiments. Comparison of genotype means showed five of the entries had grain yields in excess of 6 t/ha in the WS1 set. The check varieties Marvdasht, Cross of Alborz and Azar-2, were significantly lower yielding than most of the test lines, and ranked 18, 19 and 20, respectively. In the case of the WS2 trial, two entries had grain yield above 6 t/ha, while in the WS3 trial five entries were the best performers for yield. A subset of entries from each experiment (7 genotypes from WS1; 5 entries from WS2; and 3 entries from WS3 ) were selected for further evaluation trials. While Marvdasht can yield up to 9 t/ha under full irrigation, it will yield < 5 t/ha when irrigation water is scarce. Accordingly, we suggest the growing of the more drought tolerant lines we have identified in this study could significantly reduce this gap.

Media summary

A number of promising drought tolerant wheat varieties offer high yield potential under conditions of end-of-season drought in Iran

Key words

Water scarcity, wheat, selection, grain filling, varieties, drought tolerant

Introduction

Wheat is an this important crop occupying around 16% of the arable lands of the world, with increasing world demand and associated shortages in production in many countries. In this regard seasonal drought has always been a problem for many countries. Iran is located in a dry region which does not allow the rain fed system of crop production to perform well. Even irrigated farms are commonly under some sort of water stress especially in late spring when rainfall ceases. In future years breeding programs must consider and select from improved water use efficiency in newly released varieties. In this regard screening for more drought tolerant wheat varieties, which are able to produce an acceptable yield under one or two irrigations after rainfall ceases in spring, has became a new strategy in cereal breeding research programs. To date no variety has been released in this way, hence recent efforts have commenced during the last few years (Najafian 2003). In this study 51 lines and varieties of bread wheat, which were derived from a selection cycle for late season drought tolerance, were tested in a multi-location trial under water stress conditions applied from the heading stage onward. The objective was to develop and ultimately release varieties with enhanced drought tolerance under water stress conditions occurring in spring.

Methods

Fifty-one lines/varieties of bread wheat were planted in 3 locations (Kermanshah, Isfahan and Varamin) in 3 experiments each within a RCB design with 4 replications. These lines were divided into 3 groups based on their maturity date, with 17 entries in each group. Three check cultivars Marvdasht, Cross of Alborz and Azar-2 were also included in each experiment so that 3 sets of 20 genotypes were evaluated, as shown as WS1 – WS3. The trials were planted in early November, with plot sizes of 6 meters long and 1.2 meters wide. The harvesting area was 5 1.2 = 6 m2. Water deficits were applied to all 3 experiments in spring when there was no rainfall, and when the crop was in the heading stage. In this stage one irrigation was applied to all 3 experiments (early May 2003) and no further irrigation was then applied. After harvesting, grain yield and 1,000 kernel weight were measured for all entries across three experiments. Data were analysed as a combined ANOVA with 3 locations with 20 genotypes in each set. Means were compared using the Duncans Multiple Range Test at the 5% significance level.

Results

According to the combined ANOVA all sources of variation (location, genotype and interaction effect) were highly significant over all experiments, showing large environmental and genotypic differences existed under the conditions of this study (data not shown). It can also be inferred that the performance of different genotypes over these 3 locations was not similar, as shown in Table 1.

Table 1. Comparison of mean grain yield over 3 sites for each genotype in WS1- WS3 genotype sets.

WS1

WS2

WS3

Genotype

Mean

Genotype

Mean

Genotype

Mean

7

6.60a

36

6.27a

45

6.26a

19

6.32ab

27

6.19a

52

6.17ab

5

6.15abc

26

5.99ab

51 (Bloyka)

6.01abc

18

6.05abc

30

5.68ab

46

5.95abcd

16

6.00abc

33

5.76abc

60

5.75abcde

20

5.88abc

34

5.76abc

47

5.73abcde

11

5.87abc

25

5.64abc

48

5.71abcde

17 (Zagross)

5.85abc

28

5.63abc

41 (Marvdasht)

5.67abcde

13

5.80abc

21 (Marvdasht)

5.60abc

53

5.67abcde

10

5.76abc

31

5.51abcd

56

5.58abcde

8

5.73abc

35

5.49abcd

54

5.58abcde

15

5.700abc

39

5.43abcd

50

5.43abcde

14

5.65abc

37

5.42abcd

44

5.37abcdef

9

5.64abc

32

5.41abcd

55

5.33abcdef

4

5.52abcd

38

5.36abcd

49

5.26bcdef

6

5.46abcd

29

5.33abcd

42 (Cross of Alborz)

5.20cdef

12

5.25bcd

40

5.15bcd

57

5.05def

1 (Marvdasht)

4.95cde

24

4.90cde

58

4.9ef

2 (Cross of Alborz)

4.38de

22 (Cross of Alborz)

4.53de

59

4.51fg

3 (Azar-2)

3.96e

23 (Azar-2)

4.17e

43 (Azar-2)

4.13g

Means with unequal letters within each column have significant difference at 5% probability level.

Experiment WS1

For this experiment, comparison of means showed that entry no.’s 7, 19, 5, 18 and 16 with grain yield more than 6 t/ha were the best performers (Table 1). The check variety Marvdasht, which is mainly grown as a variety with high yield potential under full irrigation, was significantly lower yielding compared to the other test lines. Most of the test lines in this experiment were however early maturing varieties, which showed good ability to escape the drought and complete their grain filling before suffering significant end-of-season water stress. The Marvdasht variety is relatively late maturing, and needs at least 3 irrigations after the rainfall ceases in spring to complete its grain filling and hence was more affected by late season drought than the other entries. The other two check varieties (Cross of Alborz and Azar-2) which have been released for rainfed planting systems, did not show very high yield potential, being 2 – 2.5 t/ha lower yielding than the top yielding lines. Azar-2 lodged in all experiments. From this set of entries no.’s 5, 7, 10, 13, 17, 18 and 19 were selected for further adaptation trials, after considering other characteristics including resistance to yellow rust.

Experiment WS2

Genotypes 36, 27 and 26 were the best yielding entries (Table 1), although the check variety Marvdasht was not significantly different from the 8 top yielding lines. Since the test lines in this experiment were somewhat later and were similar in phenology to Marvdasht, this check variety showed an improved yield in comparison to WS1. Entry no.’s 27, 31, 32, 34 and 36 from WS2 were the selected genotypes for the proposed adaptation trial. Genotype 27 showed relatively good performance under normal conditions, thus showing wide adaptation to a range of moisture conditions, as previously observed (Rajaram 2000).

Experiment WS3

Comparison of grain yields in this experiment showed that genotypes 45, 52, 51 (Bloyka) and 46 were the top yielders (Table 1). These lines were also late maturing types and therefore Marvdasht and Cross of Alborz showed significant improvement in yield, but were still lower than some lines. From this set of entries no.’s 46, 54 and 60 were considered for inclusion in the adaptation trial based on all important traits. In this group, genotype 51 (Bloyka) was also a good performer under full irrigation conditions, and is going to be released as a new variety in the temperate zone of Iran.

Conclusion

There was common parentage for a number of the selected lines from the 3 experiments (e.g. entry no.’s 7, 10, 15 and 27 were derived from the genotype ‘Vee’. This genotype is one of the output combinations of spring winter crosses of CIMMYT, which has been recognized as a widely adapted genotype with good performance under full irrigation condition as well as tolerance to abiotic stresses of drought, heat and salinity (Villareal and Rajaram 1984, Rajaram 2000, and unpublished data in Iran). It appears that the selected lines in this study have acquired some genetic factors from this widely adapted parent and as demonstrated, by their higher grain yield in comparison to the wheat varieties with high potential of grain yield under normal conditions. Potentially the new lines could have a large impact on wheat production on irrigated farms, which are facing increasing water scarcity in spring when grain filling of wheat occurs. While Marvdasht can yield up to 9 t/ha under full irrigation, it will yield < 5 t/ha when irrigation water is scarce. Accordingly, we suggest the growing of the more drought tolerant lines we have identified in this study could significantly reduce this gap.

References

Najafian G (2003). Screening of high volume breeding lines of hexaploid wheat for drought tolerance using cluster analysis based on kernel yield and STI. Proceedings of 10th International Wheat Genetics Symposium, 1-6 Sept. Paestum, Italy.

Rajaram S (2000). International wheat breeding : past and present achievements and future directions , Warren E. Kronstad Honorary Symposium , Oregon State University Extension Service , Special Report 1017 , June 2000 .

Villareal R and Rajaram S (1984). Semidwarf Bread Wheat. Names; Parentage; Pedigrees; Origin, CIMMYT, Mexico.

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