Evaluation of tolerance to terminal drought stress in rice (Oryza sativa L.) genotypes

In order to evaluate rice genotypes for tolerance to terminal drought stress and to identifying tolerant and sensitive genotypes to this stress, 49 rice genotypes were studied in two environments (stressed and non – stressed conditions) using randomized complete blocks design with three replications in Research Field, Faculty of Agricultural Sciences, Guilan University in 2006 cropping season. The studied traits were included: plant height, panicle number plant, grain number panicle, spikelet number panicle, paddy yield, harvest index, relative water content, etc. Analysis of variance showed that there were significant effect (p < 0.01) of genotypes on all traits in two environments, which implies genetic variation among genotypes. Mean comparison of genotypes showed that in two environments, the highest paddy yield belonged to Nemat cultivar (7.31 and 7.07 t/ha respectively), whereas the least paddy yield in non - stressed environment belonged to Dom - sefid,s cultivar (2.74 t/ha) and in drought stressed environment to Diwani,s cultivar (1.46 t/ha). Considering yield components (panicle number/ plant, spikelet number/ panicle, grain number/panicle in Nemat contributed to its higher paddy yield in stressed and non - stressed conditions. Percentage of reduction in traits means by drought stress showed that the paddy yield (40%) was the most affected trait. According to drought resistant indices, the highest mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HM), stress tolerance index (STI), relative water content (RWC) and the least stress susceptibility index (SSI) and tolerance index (TOL) belonged to Nemat,s cultivar. Relationship between drought resistant indices and paddy yield in stressed and non - stressed environments showed that MP, GMP, HM, STI and RWC indices had positive and significant correlation with yield in stress and non - stress environments and would be suitable indices in both environments for selection of drought tolerant cultivars. It is concluded that STI, is the most suitable index among drought indices.