Development of rice yield components in irrigated upland and lowland environments

As water for agriculture becomes scarcer, some lowland areas will be forced to shift to upland rice cultivation. Rice generally yields less in aerobic systems. To obtain adequate yields, we need to understand the causes of reduced productivity in upland conditions and their genetic control. This chapter combines results from variety comparisons, a doubled-haploid line (DHL) mapping populations, and near-isogenic lines (NILs) to address these questions. The development of leaf area index was greater in aerobic conditions for an upland variety, Azucena, and also a lowland variety, IR72. For both varieties, the percentage of sterile grain was greater and the 1,000-grain weight less in aerobic conditions, leading to a lower harvest index in the upland field. The reduction in harvest index was more severe in the lowland cultivar. We also compared yield components measured in sprinkler-irrigated upland, furrow-irrigated upland, and lowland conditions for 85 DHLs derived from a cross between another semidwarf ndica lowland cultivar, IR64, and Azucena. Yields and most yield components were poorly correlated across upland and lowland environments. Common quantitative trait loci (QTLs) were identified across water levels for some traits, but QTLs for yield and yield components were generally specific to one environment. Additional studies ecamined the performance of NILs of IR64 that had chromosomal segments from Azucena introgressed through marker-aided selection. The introgressed segments were chosen because they contained QTLs for root traits (e.g., root thickness, length), but some yield component QTLs had also been mapped near those segments. When the NILs were cultivated under lowland conditions, they produced fewer tillers per plant than did IR64, but some produced more tillers m-2 in the uplands. Preliminary yield data indicate that some NILs can outyield IR64 in lowland and/or upland conditions. These results provide insights into the genetic control of the development of rice yield components in aerobic a d anaerobic environments.