Previous results indicated that carbon isotope discrimination (D) of the soluble carbohydrates in the peduncles of rice stems, after a drought period during panicle emergence, correlated with drought tolerance at this stage of growth. The aim of the proposed research is to develop a physiological indicator of drought tolerance and to evaluate its reliability as a tool in breeding programs for improved yield. - In order to obtain information on the relationships between water-use efficiency and d of different organs (grain, leaves and stems) and d of soluble carbohydrates in leaves and peduncles, controlled environment experiments will be performed on rice plants. Drought will be imposed at different stages of growth and compared with an irrigated control. The d values of different fractions, will be compared with gas exchange data and with 'on line' d measured on the air C02 in a gas exchange cuvette. - Field experiments comparing 20 or more genotypes, will be subjected either to drought during panicle emergence or well-watered conditions. Leaves, grains and soluble carbohydrates from peduncle tissue will be analyzed for d. The relationships between yield and d of leaves, grain and carbohydrates will be evaluated. In another type of trial, drought will be given Eor 2-3 week periods and, subsequently, the organs and soluble carbohydrates will be analyzed for d. These results will be compared with tissue water potential, in order to investigate the effects of drought on the d values of individual tissue.
In other experiments, gas exchange and 'on line' d of panicles will be measured under well-watered and drought conditions, in order to evaluate panicle Water-use efficiency and its relationship with spikelet fertility. These results should test the hypothesis that panicles have a high rate of water loss, largely insensitive to drought. The effect of drought-induced spikelet sterility on carbohydrate synthesis and source-sink relationship will be evaluated by partial or total sink removal. Apart from the intrinsic scientific interest of this important aspects 0E the physiology of rice, the proposed research should indicate whether carbon isotope discrimination of soluble carbohydrate in leaves and peduncles could be used routinely as an indicator of drought tolerance in rice breeding programs.
Funding SchemeCSC - Cost-sharing contracts
74000 Goiania - Go
CB2 1TS Cambridge