Evaluation of tolerance of rice (Oryza sativa L.) genotypes using tolerance indices and biplot analysis

In the present experiment in order to identify tolerant rice genotypes to drought stress using tolerance indices, 53 rice genotypes including 31 aerobic rice and 22 lowland rice evaluated under normal and drought stress conditions by withholding water since 30 days after transplanting of the maximum tillering stage of rice until the end of growth period on cropping seasons of 2014 in the Sangar section of Rasht. The results revealed four indices; mean productivity (MP), geometric mean productivity (GMP), stress tolerance index (STI) and yield index (YI) have the highest correlation with grain yield under normal (YP) and drought (YS) stress conditions. Grouping of genotypes using cluster analysis divided all of genotypes to three groups including tolerant, semi tolerant and sensitive. The seven genotypes contain genotypes IR81024-B-254-1-B, IR82590-B-B-32-2, IR82635-B-B-82-2, IR82639-B-B-140-1 and Panda and two lowland varieties Dorfak and Sadri assigned to tolerant group. Out of these seven genotypes, the minimum of yield loss were for IR82590-B-B-32-2, Panda and IR81024-B-254-1-B with 1.28, 4.28 and 4.86 percent yield loss.The principle component analysis on the indices showed two first components explained 58 and 40 percent (totally 98 percent) of all variation. The biplot derived from graphical analysis in addition to confirmation of cluster analysis results showed the GMP, MP, YI and STI are the best indices in detecting of tolerant genotypes. Also the best genotypes under normal condition were included Dorfak, IR82639-B-B-140-1, IR82635-B-B-82-2 and IR82590-B-B-32-2 and under drought stress genotypes of IR82590-B-B-32-2, Panda, IR81024-B-254-1-B and Dorfak identified as the best genotypes.