3.1. Cultivar experiment
Grain yield was not significantly correlated with RWC measured in the wet season, but the correlation was significant in the dry season. The correlation was strongest between grain yield in the control and stress RWC (average of measurements made after 12 and 20 days of water exclusion; Fig. 1c). Control RWC was correlated with control yield (Fig. 1a) and yield in the stress treatment was similarly correlated with RWC under stress (Fig. 1b). From the figure, it is clear that the correlation was strongly influenced by eight cultivars with low yield potential and RWC below 78%. To separate effects of yield potential from direct effects of RWC, the difference between wet season yield and dry season control yield was plotted against dry season RWC under stress (Fig. 1d). The relationship between yield reduction and RWC was negative, largely because seven cultivars had lower yields in the wet season than in the dry season. These were all cultivars from eastern India, which were affected by lodging and disease in the Philippine wet season. Other cultivars with RWC values similar to these seven cultivars had large reductions in grain yield between wet and dry seasons. The percentage of sterile spikelets in the dry season control was correlated with RWC under stress (r=−0.51,P