Genotype-by-environment interactions: RLRRC experience

Rainfed lowland rice is grown in bunded fields on 37 million ha of South and Southeast Asia, with yields averaging only 2.3 t/ha. Hydrologic conditions may fluctuate from submergence to drought, with major consequences for root growth, nutrient availability and weed competition. Because of the fluctuating conditions encountered, selection of improved cultivars is difficult. This paper examines the nature of genotype-by-environment (GxE) interactions in the rainfed lowlands, using data from nine locations in India, Thailand and the Philippines from 1995. GxE interaction accounted for 38% of the total sum of squares, with environment and genotype responsible for 48% and 14%, respectively. More than 75% of the GxE interaction sum of squares was captured in the pattern analysis. Philippine sites were rightly grouped, as were related entries. Discrimination of environments appeared to be related to general seasonal condition, and to the water regime later in the season. Groupings of entries could be explained by their performance in relation to these conditions. When conditions were more favourable, CT9897, IR20, IR36 and IR64: performed well, while Sabita, KDML1OS and IR57546 performed well in less favourable conditions. There was some evidence that NSG19 was better able to withstand a rapid onset of late-season drought, while IR66516 and IR66469 were more tolerant of flooding. Factors contributing to the patterns identified are discussed, and the results compared with those from GxE interaction studies in Thailand and the Lao People's Democratic Republic. The patterns of adaptation require further testing when the 1996 and 1997 data become available. Research is proceeding to understand the basis of these adaptation patterns, in order to assist selection of improved cultivars of rainfed lowland rice