Evaluation of Drought response in Some Rice Mutant Lines Using Stress Tolerance Indices

IntroductionDrought is a major problem that limits the adoption of high-yielding rice varieties in drought-prone rainfed rice environments. To improve crop productivity, it is necessary to understand the mechanism of plant responses to drought conditions with the ultimate goal of improving crop performance in the vast areas of the world where rainfall is limiting or unreliable. Safaei Chaeikar et al. (2008) reported that MP, GMP, HM and STI indices, which showed the highest correlation with grain yield under both optimal and stress conditions, can be used as the best indices to introduce drought-tolerant genotypes in rice breeding programs. They also were introduced Nemat, Sepidrood, IR64, IR50 and Bejar genotypes as tolerant varieties. The present study was conducted to determine how drought affects grain yield in rice mutant lines and also to test this hypothesis in order to identify the most suitable indices/genotypes.
Materials and MethodsA field trial was conducted at Iranian Rice Research Centers in North of Iran, Rasht (latitude 37◦28', longitude 49◦28'E and altitude 7m below the sea level), during the 2014-2015 growing season. The seeds were sown in a nursery on the 10 May and 25 day old seedlings were transplanted to the field. Two separately experiment was carried out under reproductive stage drought stress and controlled conditions based on randomized complete block design with three replications, in four-row plots of three m length. Transplanting was done using 1 seedling per hill; at hill spacing of 25 cm × 25 cm. 18 rice genotypes were consisted 14 M5 mutant lines and their four parental cultivars.
Results and DiscussionAnalysis of variance indicated significant effects of drought stress, genotype and interaction effects of two factors on grain yield, plant height, flag leaf area, tiller number and grain fertility percentage. Drought stress at reproductive stage caused reduction in grain yield (59.47%), grain fertility percentage (19.08%), plant height (9.35%), flag leaf area (8.59%) and panicle length (1.61%). Different drought indices probably measure similar aspect of drought tolerance/resistance. Significant yield reduction was observed under drought stress in majority of the rice genotypes studied. Drought tolerance indices were varied significantly indicating genotypic variability. Selection based on these stress tolerance indices will results in identification of drought tolerant genotypes for rainfed ecosystems. The stress tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP) and harmonic mean (HM) were superior in genotype indicating that they can be used as alternative for each other to select drought tolerant genotypes with high yield performance in both stress and non-stress conditions. To determine the most desirable drought tolerance criteria, the correlation coefficients between Yp, Ys and other quantitative indices of drought tolerance were calculated. The results indicated that there were positive and significant correlations among Yp and MP, GMP, STI and HM. There were also significant and positive correlation between Ys and YI,HM,GMP,YSI,STIandMP. In this experiment, the principal component analysis was performed on eight indices and grain yield under stress and non-stress in 18 rice genotypes. Results showed that the first two components explained 82.8% and 17% of total variation, respectively. The relationship between principal components and studied indices showed that the higher values of first and the lower values of second components were related to drought tolerance and sensitivity to stress, respectively. Selection based on a combination of indices may provide a more useful criterion for improving rice drought-tolerant lines; therefore, studies of correlation coefficients are useful in finding out the degree of overall linear association between any two attributes. According to these drought stress indices, G1, G2, G3, G4 and G5 (M5 mutant lines of local lanrace, Tarom) and (M5 mutant line of Hashemi) were as drought tolerant and G14 (mutant lines of Khazar), G15 (Hashemi), G16 (Khazar) and G17 (Tarom) were sensitive to drought stress.
ConclusionsResults of present study showed that MP, GMP, YI and STI are best indices for selecting and specifying of rice tolerant genotypes in arid areas. The use of mutation caused drought resistant on the progenies and the above lines can be used in a project of introduction of drought tolerant rice varieties.