Responses of seven diverse rice cultivars to water deficits I. Stress development, canopy temperature, leaf rolling and growth

Abstract

Predawn and midday leaf water potentials and leaf osmotic potentials, soil water potentials, canopy temperatures, leaf rolling, light interception, dry matter production and water use were followed in seven rice (Oryza sativa L.) cultivars before, during and after the imposition for 10 days of different irrigation treatments by a line source sprinkler system imposed prior to flowering. The seven rice cultivars, Azucena, Tachiminori, IAC 25, IRAT 13, BPI 76, IR 20 and IR 36, represented a wide range of germplasm from traditional dryland to improved wetland types. As soil water potentials in the upper 30 cm of the soil decreased, canopy-to-air temperature differences increased, leaf rolling increased and dry matter production decreased. The wetland cultivars IR 20 and IR 36 had a greater diurnal change in leaf water potential between predawn and midday than the dryland cultivars. Canopy-to-air temperature differences and leaf rolling scores also varied among cultivars. Leaves of the dryland cultivars, particularly Azucena and IAC 25, rolled and had higher canopy-to-air temperature differences at higher waterpotetials and higher turgor pressures than the wetland cultivars IR 20 and IR 36. No differences among cultivars were observed in either the rates of dry during the period of differential irrigation. The stress treatments imposed in the pre-flowering period delayed panicle emergence by 10 days in IAC 25 which was at the boot stage of development, when stress was most severe, and by 4 to 5 days in all other cultivars, some of which emerged up to 30 days after full irrigation had been restored. The results suggest that the physiological differences observed among cultivars, particularly between wetland and dryland types, had little effect on growth and water and water use during a short period of water deficit.