EFFECT OF WATER-DEFICIT STRESS ON DIFFUSIVE RESISTANCE, TRANSPIRATION, AND SPIKELET DESICCATION OF RICE (ORYZA-SATIVA L)

To unerstand the nature of panicle resistance to water loss, diffusive resistance, transpiration rate, and degree of tissue desiccation were studied as affected by low tissue water potentials and relative water contents (RWC) induced;by water deficit stresses. A drought susceptible cultivar (IR20) and a moderately resistant cultivar (IRAT 13) were;compared under moderate and severe water deficit stresses under greenhouse conditions. Irrigation was withdrawn;at flowering stage. During the 10-d stress period, changes in panicle and flag leaf transpiration and white head;formation (desiccated) were monitored. Using cut panicles transpiration and white head formation at different RWC;levels in 11 different cultivars were also measured. In flag leaves, increased diffusive resistance and leaf rolling reduced;transpirational losses from the adaxial surfaces. Leaf resistance and rolling were linearly correlated with leaf water;potentials. Resistance in panicles increased with progressive decline in water potentials, but the change was not as high;as in leaves.Among test cultivars, diffusive resistance increased at the late flowering stage but not at the early stage when panicles were newly emerged. Increased water losses contributed to severe spikelet desiccation and white heads. A few;of the upland cultivars tested, such as Kinandang Patong, IRAT 140 and IRAT 13 conserved more water and showed;reduced water-deficit stress symptoms. © 1993 Annals of Botany Company.