Genetic variation in performance under reproductive-stage water deficit in a doubled haploid rice population in upland fields

Water deficit at the flowering stage causes dramatic reductions in rice yield. Screening for tolerance to water stress at this stage is complicated by differences in flowering dates among lines and technical problems of imposing uniform, repeatable experimental conditions. The objectives of this work were to document genetic variation in tolerance to water deficit during flowering and grain filling among doubled haploid rice lines (DHL) from a japonica-by-indica cross, to identify genetic markers associated with performance, and to identify secondary traits that cosegregate with yield or yield components. In one season, staggered planting dates were used to synchronize flowering. In a second season, rice was grown using furrow irrigation and two periods of moderate water deficit were imposed in order to stress all entries at the most sensitive stage. In both seasons, stress treatments affected the percentage of sterile spikelets and the weight per grain. Quantitative trait loci (QTLs) were identified for yield components in each season and water level. A few QTLs had consistent effects across environments and/or seasons, but others were specific to the measurement environment. Across years, the QTLs identified for yield components under stress were not identified in the control, indicating that spill-over effects are not adequate to exploit the genetic potential for yield under stress that is present in this population. On the other hand, the interval containing the sd1 gene appears to have a major effect on sterility, yield and harvest index under varied conditions. Some QTLs for yield components under stress cosegregated with reported QTLs for drought-adaptive traits such as root depth and thickness. (Résumé d'auteur