Assessment of wheat yield response to water shortage using various tolerance indices

Thirty-nine bread wheat (Triticum aestivum L.) genotypes were tested for their tolerance to late season drought stress during 2011 and 2012. The experiment was conducted under two different irrigation conditions of (a) normal irrigation and (b) late season drought stress, where irrigation was cut off after heading stage. Each of the two experiments was conducted in a randomized complete block design with three replications. The combined analysis of variance showed significant difference among genotypes, environments and genotype x environment interaction. Eleven drought tolerance indices including stress susceptibility index (SSI), tolerance index (TOL), mean production (MP), stress tolerance index (STI), harmonic mean (HM), relative drought index(RDI), geometric mean production (GMP), yielded index (YI), yield stability index (YSI), drought resistance index (DI), and stress susceptibility percentage index (SSPI) were calculated based on grain yield under drought (Ys) and irrigated conditions (Yp). Yield under stress (Ys) and non-stress (Yp) conditions were significantly positively correlated with STI, GMP, MP, HM, and YI in both years. Results showed that indices of stress tolerance/resistance such as STI, GMP, MP, HM and YI can be used as the most suitable indicators for screening drought-tolerant cultivars. Screening drought-tolerant cultivars using ranking method discriminated cultivars Akbari, Roshan and Alvand as the most drought-tolerant in both years. Other cultivars identified as drought-tolerant were Kavir, Ws-82-9, Hirmand, Moghan2, Dez, Star, and Atrak in the first year, and Pishtaz, Sardari, Qods, Azadi, Toos, Sabalan, Shole and Tajan in the second year.In terms of mean yield and drought tolerance indices, genotype Alvand (3.44 t/ha) was identified as the most favorable candidate.