Changes at panicle emergence in the water relations of a wetland and a dryland Japonica rice cultivar under wetland conditions

The diurnal and seasonal changes in plant water relations of two Japonica rice (Oryza sativa L.) cultivars, Nipponbare and Tachiminori, were studied under flooded conditions at Kyoto University. The dryland cv. Tachiminori maintained higher predawn and midday leaf osmotic potentials relative to the wetland cv. Nipponbare during the vegetative stage, but the ranking was reversed after flowering. The relationship between leaf water potential and leaf osmotic potential showed that prior to panicle emergence Nipponbare was able to adjust osmotically to maintain turgor, whereas after heading there was little turgor maintenance. Tachiminori showed little difference in osmotic adjustment before and after panicle emergence. Fertilizer treatment during panicle development also helped to maintain the degree of osmotic adjustment in both cultivars.