Abstract

A series of experiments were conducted under normal and drought conditions to examine the magnitude of yield response of diverse genotypes to drought stress and to identify traits that may confer drought resistance. Thirty-three local and exotic rice entries including 18 Egyptian genotypes (selected from Fn generation of the breeding for drought tolerance program, Rice Research and Training Center, Egypt), six Italian and nine Chinese rice varieties were grown at Rice Research and Training Center experimental farm for evaluation under normal as well as drought conditions during 2007 and 2008 rice growing seasons. Experiments were laid out in randomized complete block design with three replications. Analysis of variance indicated highly significant differences among the genotypes for all the traits studied.  Many promising lines were found to be tolerant against drought stress at different growth stages i.e. seedling stage, early and late vegetative stage, panicle initiation stage and heading stage. These lines possess useful traits associated with drought tolerance such as early maturity (drought escape mechanism), medium tillering ability, medium  plant height,  root depth, root thickness, root volume, dry root: shoot ratio, plasticity in leaf rolling and unrolling (drought avoidance mechanism), in addition to crop water use efficiency and water application efficiency. The results showed that the genotypes viz: Giza 178, Giza 182, GZ5121, GZ 6296-12-1-2-1-1, GZ 8310-7-3-2-1, GZ 8367-11-8-3-2, GZ 8372-5-3-2-1, GZ 8375-2-1-2-1, GZ 8450-19-6-5-3, GZ 8452-7-6-5-2, GZ 1368-S-4, Augusto and SIS R215  were the best entries under drought conditions, where they  possess many desirable traits which  are useful for drought tolerance. Among the traits studied viz: number of tillers per plant, number of panicles per plant, 100 grain weight, panicle weight, revealed significant genotypic correlation with grain yield. Also, number of filled grains per panicle depicted the highest direct contribution of 0.630 and it also show highest indirect contribution of 0.867 followed by 100 grain weight (0.850) towards grain yield. Path coefficient analysis demonstrated that number of panicles per plant, 100 grain weight; number of filled grains per panicle, panicle weight should be improved in order to increase grain yield under both normal and drought conditions.

Key words:  Drought stress, path analysis, rice, screening.