Rice Genetics IV - IRRI books - International Rice Research Institute

For drought-response screening, our objective is to identify mutant lines that affectthe transduction of stress signals that influence grain filling under stress. In 1999,1,200 mutant lines were evaluated for yield under continuous flooding and with floodwaterdrained prior to flowering. The stress treatment delayed flowering by 2 d andreduced yield by about 28%. After using spatial analysis to compensate for variationwithin the field, we identified 65 lines with superior yield in either the stress or controltreatment. These lines were evaluated in replicated experiments in 2000; theydiffered significantly in yield in both the control and stress plots, but the stress treatment(field drained 18 d after panicle initiation) had little effect on yield because ofunseasonable rain. An additional 1,200 deletion lines were evaluated in 2000. Theywere uniform in appearance and flowering date. Under stress, some variation in senescencerate was observed. Based on visual scores and on grain yields under stressrelative to the IR64 check, 26 lines were identified for further assessment of variationin component traits related to tolerance of late-season stress (R. Lafitte, unpublisheddata, Fig. 3).Opportunities for other traitsResults from screening for phenotypic variation in morphology and responses to bioticand abiotic stresses suggest that the IR64 population is rich in genetic variability.Yield under stress (t ha –1 )987LinesChecks65432100 1 2 3 4 5 6 7 8Control (t ha –1 )Fig. 3. A scatter plot of yield response of IR64 mutants to water stress atthe IRRI farm. Mutant lines were grown under water stress and controlconditions. The irrigated control was flooded a few weeks later and remainedwith 5–10 cm of standing water until about 1 wk before harvest.The water-stress block was flooded a few weeks after transplanting butwas drained 1 wk before flowering; thus, plants were under stress duringgrain filling. Accelerated senescence was observed in the stress. Grainyield (t ha –1 ) was extrapolated from plot-size yield. Wide deviation from the1:1 slope suggests a contrasting performance under the two environments.246 Leung et al