ارزیابی شاخص‌های تحمل به تنش خشکی در ژنوتیپ‌های برنج (Oryza sativa L.)

Drought stress is one of the most important abiotic stresses in crops that can reduce yield and yield components in terms of time, duration and severity of the stress. Current research was carried out in order to evaluate drought stress tolerance in rice genotypes. Experiment done in two separate schemes using randomized complete blocks design with three replications in Research Field, Faculty of Agricultural Sciences, Guilan University in 2006. Irrigation was conducted equally as flooding until the beginning of tillering stage of genotypes in both stressed and non-stressed conditions, then irrigation was completely cut off in stressed condition, while it was full until the end of maturity in non-stressed condition. Results of mean comparison of different tolerance and susceptible indices based on paddy yield introduced Araguiua, Diwani, Domsefid, Dom sorkh and Hasan Saraei Atashgah as susceptible genotypes which these genotypes were the highest sensitivity to drought and produced the lowest paddy yield (1.68, 1.48, 1.82, 1.96, 2.14 ton/ha respectively). Also genotypes such as Nemat, Sepidrood, IR64, Bejar and IR50 showed the highest tolerance to drought stress and have the highest paddy yield (7.07, 4.59, 4.04, 4.03 and 4.38 ton/ha respectively), so that these genotypes are recommended for planting in dried conditions, as well as, cross parents for increasing drought tolerance of commercial variety. Results of principle components analysis identified two main components in drought conditions that were explained more than 98% of the variance of indices. Drawing by- plot based on two main components showed that the first component had high and positive correlation with YS, YP, MP, GMP, HM and STI, so it named as yield potential and drought tolerance. The second component had positive correlation with RDI and DRI indices and is called as drought response. Cluster analysis based on all studied traits using Ward method attributed genotypes into four groups. The estimation of groups mean and their differences from genotypes total mean showed that there were significant differences between groups for physiological and morphological traits.