Elsevier

Field Crops Research

Volume 64, Issues 1–2, November 1999, Pages 131-151
Field Crops Research

Rainfed lowland rice breeding strategies for Northeast Thailand.: I. Genotypic variation and genotype × environment interactions for grain yield

https://doi.org/10.1016/S0378-4290(99)00056-8Get rights and content

Abstract

The magnitude and nature of genotype-by-environment (G × E) interactions for grain yield, days-to-flower and plant height of rainfed lowland rice in Northeast Thailand were examined using random F7 lines from seven crosses developed by the Thai breeding program. A total of 1116 lines and checks were evaluated in a multi-environment trial conducted across three years (1995–1997) and eight sites. The G × E interaction was partitioned into components attributed to genotype-by-site (G × S), genotype-by-year (G × Y) and genotype-by-site-by-year (G × S × Y) interactions. The G × S × Y interaction was the largest G × E interaction component of variance for all three traits. There was little G × S interaction for grain yield and days-to-flower. The G × S interaction was significant for plant height, but was the smallest component of variance for that trait. The G × Y interaction component of variance was significant for all three traits, but was small relative to the genotypic component for days-to-flower and plant height. For grain yield the G × Y interaction component was comparable in size to the genotypic component. Partitioning the genotypic and G × E interaction components of variance into among-cross and within-cross components indicated that there was significant variation both among and within the crosses for each trait. The relationships between the three traits differed among the crosses and the environments. A major factor contributing to the large G × S × Y interactions for grain yield was the genotypic variation for days-to-flower in combination with environmental variation for the timing and intensity of drought. Some of the interactions associated with timing of drought were repeatable across the environments sampled in the multi-environment trial, and to some extent the environments were characterised on the basis of whether there was pre-flowering, intermittent, or terminal drought. There was genotypic variation for grain yield after taking into consideration the influences of timing of drought in relation to plant development. Three of the seven crosses involved the Thai cultivars KDML105 and RD6 as parents. These crosses produced an array of progeny with lower yield than the Thai cultivars, suggesting it would be difficult to improve on the yield of these cultivars. In contrast three of the remaining four crosses, which did not have a Thai cultivar as a parent, produced progeny that had higher yield than KDML105 and RD6 indicating that yield of rainfed lowland rice could be improved above that of the these popular cultivars.

Introduction

Investigations of genotypic variation and genotype-by-environment (G × E) interactions for grain yield of rainfed lowland rice have been conducted in and across a number of Asian countries (Henderson et al., 1996; Cooper and Somrith, 1997; Wade et al., 1997, Wade et al., 1999). Generally these studies used sets of lines that had been selected to represent recognised genotypic diversity for adaptation to a range of the rainfed lowland rice ecosystems. A major objective of these exploratory studies was to investigate environmental and genetic constraints to the improvement of broad and specific adaptation of rainfed lowland rice for a range of target environments (Cooper, 1999). An understanding of these constraints was sought as a basis for defining breeding strategies that would contribute to higher and more stable grain yields for the heterogeneous rainfed lowland ecosystems. These studies consistently identified large crossover type G × E interactions for yield. The presence of these interactions has important implications for breeding strategies that aim to improve either broad or specific adaptation or some combination of both components of adaptation. Crossover G × E interactions can be a significant impediment to selection strategies that aim to improve broad adaptation. Alternatively, where some aspects of the G × E interactions are repeatable, it may be possible to select for components of specific adaptation to the relevant target environments. It has been argued that a breeding program aimed at recombining components of specific adaptation to drought environments may be a strategy for improving drought resistance and broad adaptation of rainfed lowland rice (Fukai and Cooper, 1995; Nyguen et al., 1997; Cooper, 1999).

The use of selected sets of diverse lines in the previous adaptation investigations makes it difficult to evaluate the implications of their results for the design and optimisation of crossing and selection strategies within a breeding program. To enable this step it is necessary to obtain estimates of the magnitude and form of genetic, G × E interaction and error components of variation that are relevant to both the target population of environments and the germplasm used in the breeding program. The focus of the present study is to investigate the implications of G × E interactions for genetic improvement of the grain yield of rainfed lowland rice in drought-prone Northeast Thailand. The objectives were to: (1) document the magnitude of sources of genotypic, G × E interaction, and error variation for grain yield, based on a sample of breeding lines relevant to the Thai breeding program for Northeast Thailand; (2) examine the influence of timing of drought and genotypic variation for flowering time and plant height on G × E interactions for grain yield; and (3) evaluate potential sources of repeatable G × E interactions for grain yield. A companion paper (Cooper et al., 1999) evaluates suggested modifications to the current breeding strategy used in Northeast Thailand.

Section snippets

Reference population: development of experimental lines

Seven biparental crosses were sampled from the crossing program of the Thai rainfed lowland rice breeding program in 1992 (Table 1). A series of random inbred lines were derived from each cross. These inbred lines, their parents, the five check cultivars KDML105, RD6, RD23, NSG19, Chiangsaen, and one check line IR57514-PMI-5-B-1-2, were used as the experimental lines in the multi-environment trial (MET). Seed was not available for one of the parents of Cross 4, NR15013-40-10-7, so this line

Experimental conditions and environmental characterisation

The seeding and transplanting dates of the experiments differed among the site–year combinations (Table 3). In each of the three years, two experiments were seeded late. With early seeding and no drought or stress conditions (e.g. 1995 PSL), the time from seeding to flowering was longer for the strongly photoperiod sensitive check lines. As expected with later seeding, the differences in flowering time between the strongly photoperiod sensitive and less sensitive check lines decreased and in

Discussion

The analysis of the sources of variation based on the results of the METs identified significant components of genotypic, G × E interaction and error variation for the traits grain yield, days-to-flower and plant height. Partitioning the G × E interaction component indicated that the three-factor G × S ×Y interaction was consistently the largest source of G × E interaction for all three traits. The G × S × Y interaction was 4.3 times the size of the genotypic component of variance for grain yield, but for

Acknowledgements

The contributions and commitment of the many Thai scientists involved in conducting the experiments is gratefully acknowledged. The Australian Centre for International Agricultural Research provided the financial support for conduct of the experiments.

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