Assessment of Tolerance to Drought Stress at Reproductive Phase in Some Wheat Genotypes (Triticum aestivum L.) Using Drought Tolerance and Susceptibility Indices

Wheat is important plant in the economy of the world. Between wheat cultivars, bread wheat (Triticum aestivum L.) is the best cultivar for nutrition. Drought stress led to decrease production, therefore, it causes problems for nutrition and agriculture. Iran is located in dry belt of the earth and its annual rain average is 250 mm. In dry land, grain filling phase is faced with a warm season when the air temperature is high and soil water storage is reduced. For screen best drought tolerant genotypes must use from drought tolerance and susceptibility indices. The purpose of this research was to identify and determine drought tolerant and high yield lines for introduction in drought stress conditions during reproductive phase and to determine the indices with a desirable efficiency for evaluating reaction of genotypes to stress conditions.
Materials and Methods: An experiment based on randomized complete bock design with three replications was conducted Torogh Mashhad Agricultural Research Stations, Iran, during 2014-2016 growing seasons. In this research eight genotypes of winter wheat with three control cultivars of Mihan, Orum, zare were compared under two conditions of full irrigation and water stress during reproductive phase. Statistical analysis was performed by using SAS and SPSS software. After harvesting, yield and indices drought tolerance indices including SSI (Stress Susceptibility Index), STI (Stress Tolerance Index), GMP (Geometric Mean Productivity), HARM (Harmonic Index), MP (Mean Productivity), YSI (Yield Stability Index), YI (Yield Index), DI (Drought Index), MSTI (Modified Stress Tolerance Index), ATI (Abiotic Tolerance Index), SSPI (Stress Susceptibility Percentage Index), RE% (Reduction Percentage), SNPI (Stress non-Stress Production Index), TOL (Tolerance).

 Results showed that the effect of year, genotype and irrigation and interaction effect between year and genotype were significant on all of studied traits. Drought stress decreased yield of genotypes about 32% and 30% in the first and second year, respectively. Other investigation showed that drought stress at the reproductive phase led to reduce current photosynthesis and high respiration. According to Fernandez, indices that have a significant correlation with grain yield in both stress and non-stress conditions are superior indices because they are able to distinguish high-yield genotypes in both conditions. In our research there was a significant and positive correlation between GMP, MSTI, HM, STI, MP with grain yield in both non-stress and stress conditions. In drought stress conditions genotype 8 and 9 ranked had the highest yield (5176 and 5079 kg ha-1), and were selected as the most tolerant genotype.

This research showed that drought stress at the reproductive phase reduced grain yield. GMP, MSTI, HM, STI and MP showed significant and positive correlation with grain yield in both non-stress and stress conditions. Genotype 8 had the highest rank in all of the mentioned indices, it could be considered as tolerant genotype to the drought stress at the reproductive phase due to the proper grain yield in both stress and non-stress conditions.