Relationship between leaf relative water content during reproductive stage water deficit and grain formation in rice

Data from field trials using cultivars, a mapping population, and a set of BC3 introgression lines were used to examine the relationship between plant water status (measured as leaf relative water content, RWC) and yield and spike-let sterility (%SS) for aerobically grown rice exposed to water deficit during the reproductive stage. Control plots were irrigated several times each week to maintain soil moisture near field capacity, while stress plots experienced periods of soil drying. In an experiment comparing 35 lines and cultivars, control grain yield in the dry season was correlated with RWC measured during a period of water exclusion (r = 0.72, P < 0.01). This correlation was strongly influenced by genetic differences in yield potential and maturity. In a mapping population comprising approximately 80 lines, leaf RWC in the irrigated control was significantly correlated with %SS (r. = -0.43, P < 0.01) and yield (r = 0.45, P < 0.01). No correlation was observed between leaf RWC at the end of a 14-day stress period and %SS or yield in stress plots. In a set of BC3 introgression lines, RWC was not associated with yield or %SS in either stress or control treatments. Leaf water status appears to be related to yield and %SS in some cases, but the relatively weak cotrelations indicate that other characteristics of the lines are also important in determining the integrated response to reproductive stage drought stress. When the range of contrasting characteristics was reduced through the use of introgression lines, the association between yield and RWC disappeared, even though lines differed significantly in their yield response to water deficit. (C) 2002 Elsevier Science B.V. All rights reserved.