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Increasing crop-water productivity through genetic improvement for tolerance to water stresses in maize (Zea mays L.)

Pervez H. Zaidi1, Ganesan Srinivasan2 and N.N. Singh1

1 Directorate of Maize Research (DMR), IARI campus, New Delhi, India,
2
International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, 00660 Mexico, D.F. Mexico,
* For correspondence: phzaidi@yahoo.com (P.H.Zaidi)

Abstract

Inadequate water is a major cause of crop yield losses particularly in the tropics. Uncertainties in weather due to global warming are expected to increase the occurrence of inadequate water availability. At CIMMYT, various approaches to improved drought tolerance in maize have been explored. About three decades of work on drought tolerance in maize has resulted in improved source populations and open-pollinated and hybrid products that perform well under drought stress. Results from recent studies show the usefulness of this germplasm under severe drought stress conditions. Furthermore, the improvement for mid-season drought tolerance appears to impart tolerance to various other stresses, such as low-N fertility. Under ICAR-CIMMYT collaborative program, a large amount of maize germplasm, including inbred lines from CIMMYT and the national program, were screened for excess moisture/waterlogging tolerance in India. Many promising tolerant lines were identified and further improved for developing excess moisture tolerant cultivars for waterlogging prone areas in India. The secondary traits such as anthesis-silking-interval (ASI), early and increased brace root development and high root porosity have been identified the traits associated with excess moisture tolerance in maize. Due to fairly high expression of the stress-adaptive traits under managed drought or excessive moisture stress conditions, they can be carefully selected and further improved. Since the maize is frequently exposed to both the extremes of water availability in many monsoonal areas in Asia, our major focus is to develop robust germplasm with improved performance across the regimes of water availability.

Media summary

New maize varieties for Asia can tolerate drought and waterlogging, thanks to the combined skills of plant breeding and plant physiology.

Key Words

Drought tolerance, maize, breeding, waterlogging, nitrogen.

Introduction

Among abiotic stresses, drought or excessive soil moisture are the major limiting factors for maize productivity in tropics. The normal inter-seasonal fluctuations in rainfall are associated closely with variations in average national maize yields across quite large production regions in the tropics (Edmeades et al 1995), suggesting that water stress is the pervasive cause of yield instability in maize-based cropping systems in most years in the tropics. In South-East Asia, about 15% of total maize growing areas are affected by floods and waterlogging problems, causing losses in maize production of 25-30% almost every year (Rathore et al 1998). Major progress on tolerance to both the water stresses in maize has been made through a physiological-breeding approach. In this paper, we discuss the progress in developing water stress tolerance in maize at International Maize and Wheat Improvement Center (CIMMYT) and Directorate of Maize Research (DMR), India using conventional and physiological-breeding approaches, and the importance of the improved maize germplasm in increasing maize productivity with stability across the stressed and unstressed environments.

Progress with recurrent selection for drought tolerance in tropical maize

In order to estimate the current status of progress with S1-recurrent selection scheme and possibilities of further improvement, experiments were conducted in large plots at Tlaltizapan during the rain–free winter season of 2002-2003, under two water regimes, i.e. well-watered (WW) and severe drought stress (SS). Yield gains in La Posta Sequia and DTP averaged 218 and 239 kg ha-1 cycle-1 under SS, and 55 and 41 kg ha-1 cycle-1 under WW conditions, respectively (Table 1). Yield improvements under drought were paralleled by increases in ears plant-1 and harvest index, while ASI declined. Conventional selection, at mainly well-watered sites, only improved yield under well-watered conditions (Byrne et al 1995). Principal component analysis of yields in the 10 environments showed that well watered and droughted environments were generally orthogonal (Chapman et al 1997), which indicates that selection under well-watered environments is unlikely to give yield improvements under drought. Chapman et al. (1997) concluded from these and other analyses that selection for drought tolerance has improved broad adaptation, as well as specific adaptation to dry environments.

Table-1: Grain yield and other traits of La Posta Sequia and DTP improved for mid-season drought tolerance.

 

Yield (t/ha)

Anthesis (days)

ASI (days)

Ears per plant

Harvest index

Germplasm

DR

WW

DR

DR

DR

DR

             

La Posta Seq. C0

1.87

8.24

84.30

6.40

0.77

0.10

La Posta Seq. C3

2.43

8.26

83.40

4.40

0.85

0.18

La Posta Seq. C6

2.55

8.39

82.20

3.90

0.92

0.17

La Posta Seq. C8

2.62

8.42

82.90

3.30

0.99

0.19

Population 43 C9A

1.74

8.00

86.10

7.00

0.79

0.09

             

DTP2 C0

2.32

7.83

80.22

3.80

0.91

0.22

DTP2 C3

2.36

7.88

80.16

3.33

0.92

0.23

DTP2 C5

2.48

8.03

80.26

3.07

0.95

0.24

DTP2 C6

2.43

7.90

81.21

2.82

0.97

0.22

DTP C9 W

2.62

8.34

81.60

2.73

1.01

0.24

DTP C9 Y

2.53

8.24

81.09

2.71

1.00

0.23

Tuxpeno Seq. C8A

2.29

7.76

80.0

3.90

0.93

0.22

             

Gains cycle-1

           

La Posta Seq.

0.218**

0.055ns

-0.57**

-1.09**

0.10**

0.05**

DTP

0.239**

0.041**

-0.49**

-0.94**

0.42**

0.03**

   

**, * Indicate that gains were significantly different at P<0.01 and P<0.05, respectively. A Base populations.

Selection gains across multiple environments

Gains with selection under mid-season drought stress (cf under optimal input conditions) in DTPs (Fig.1) were remarkable for drought (89.6%), and also for low-N stress (39.3%). Improved performance of DTP hybrids across the environments was related to improvements in secondary traits under stress conditions - reduced ASI, increased ears per plant, delayed senescence and relatively high leaf chlorophyll during late grain filling stage (Zaidi et al 2003). Correlation and regression analysis showed a strong relationship between grain yield under drought and low-N stress in the germplasm improved for mid-season drought tolerance. However, with germplasm improved for yield per se under optimal conditions (the NSC hybrids), both linear regression and correlation between drought and low-N stress were non-significant.

Fig. 1: Relationships between grain yield under drought (SS) and low nitrogen stress in DTP- top crosses from DTP c9 S3, improved for nine cycles for tolerance to mid-season drought, and in NSC-hybrids, improved for high yield under optimal growing conditions.
(* Significant at P<0.01; ns indicates non-significant at P<0.05).

Excessive moisture (waterlogging) tolerance in maize

A project on excessive moisture tolerance in maize was launched during mid-90s under ICAR-CIMMYT collaborative program; work at DMR Headquarters was initiated in 1998. Attempts were made to identify the most susceptible crop stages, important secondary traits associated with the stress tolerance and tolerant sources of germplasm, and to develop suitable screening techniques. The status of progress and achievements along with experimental details are described below:

i) Susceptible crop stages:

In order to identify the most susceptible growth stage(s) an experiment was conducted during summer rainy season 1999, and repeated again during 2000 at maize research farm, DMR, New Delhi, India. Significant variability was observed at different physiological stages in the extent of damage caused by stress condition. The largest effect was observed at V2-stage followed by V7-stage, and was least on R1-stage for all the parameters studied. The crop susceptibility index was highest at V2-stage followed by V7-stage. Susceptibility to excess moisture stress generally declined with progress of crop growth, and it was least at R1-stage.

ii) Identification of tolerant germplasm and important secondary traits:

Using the technique mentioned, a total 324 tropical/sub-tropical lines (S4-Sn) from the All India Co-coordinated Maize Improvement Project (AICMP), New Delhi, India and CIMMYT were screened in kharif 2002. Genotypes were grouped into five categories using a multi-traits selection index i.e. highly tolerant (HTL), tolerant (TL), moderately tolerant (MTL), susceptible (SUS) and highly susceptible (HSUS). Most of the genotypes grouped under HSUS and SUS categories, however, seven entries, including 4 CIMMYT lines and 3 from the national program were identified as HTL, and 12 were TL. The promising excess moisture tolerant lines were further improved and used in breeding for development of excess moisture tolerant cultivars.

Conclusion

Our results suggest that improved stable yields can be achieved in tropical regions with selection and improvement of germplasm on the basis of performance under mid-season drought. Genetic gain may be relatively slow, but should lead to more stable production across environments. Improvement for mid-season drought tolerance has significant spillover effect towards low-N tolerance, but not vice-versa. Effective selection depends on the availability of facilities where stress can be carefully controlled, and where rainfall does not interfere with stress at flowering. Our findings suggest that excessive moisture stress is highly detrimental to maize before tasseling. However, there is considerable genotypic variability in tolerance, both at seed germination and early seedling stage, and also at V6-V7 growth stage. Early and increased adventitious rooting, enhanced root porosity and reduced ASI (<5 days) along with grain yield can be used in selection index to identify of waterlogging/excess moisture tolerant maize genotypes. The scope for genetic gains is tremendous for both drought and excess moisture tolerance. This can be exploited in systematic manner, but not through the conventional approach of testing in a random sample of environments.

References

Byrne, P. F., Bolanos, J., Edmeades, G. O., Eaton, D. L. 1995. Gains from selection under drought versus multilocation testing in related tropical maize populations. Crop Science, 35, 63-69.

Chapman, S. C., Crossa, J., Edmeades, G. O. 1997. Genotype by environment effects and selection for drought tolerance in tropical maize I. Two-mode pattern analysis of yield. Euphytica, 95, 1-9.

Edmeades, G. O., Banziger, M., Chapman, S. C., Ribaut, J. M., and Bolanos, J. 1995. Recent advances in breeding for drought tolerance in maize. Paper presented at the West and Central Africa Regional Maize and Cassava Workshop, May 28-June 2, 1995, Cotonou, Republic of Benin.

Rathore, T.R., Warsi, M.Z.K.,.Singh, N.N., Vasal, S.K., 1998. Production of Maize under excess soil moisture (Waterlogging) conditions. 2nd Asian Regional Maize Workshop PACARD, Laos Banos, Phillipines, Feb 23-27, 1998 pp 23.

Zaidi, P.H., Srinivasan, G., Cordova, H. and Sanchez, C. 2003. Gains from selection for mid-season drought tolerance in tropical maize. Paper presented at Arnel R. Hallauer International symposium on plant breeding, held at CIMMYT Mexico, Aug 17-22, 2003.

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