evaluation of heat stress tolerance indices in wheat

continual heat stress affects approximately 7 million hectares of wheat in developing countries, while terminal heat stress is a problem in 40% of temperate environments, which cover 36 million hectares throughout the world. heat tolerance is a quantitative and complex trait that doesn’t have much success in direct selection. for this purpose, however, a thorough understanding of physiological responses of plants to high temperature, mechanisms of heat tolerance and identification of screening indices for development of heat-tolerant genotypes is imperative. to assess heat tolerance indices in wheat, 144 recombinant inbred lines derived from the cross of kauz (heat tolerant) and mtrwa116 (susceptible) together with some commercial cultivars were evaluated during 2006–2007, 2007–2008. the experiments were carried out through a rectangle lattice design (12×13) with two replications in research field of college of agriculture and natural resources, persian gulf university, borazjan, bushehr, iran. genotypes were planted under normal and heat stress (late sowing) conditions. plant height, peduncle length, head length, spiklets per spike, kernels per spike, grain filling duration, 1000 kernels weight and grain yield were measured. eight stress tolerance indices including stress susceptibility index (ssi), tolerance (tol), geometric mean productivity (gmp), mean productivity (mp), stress tolerance index (sti), yield stability index (ysi), yield index (yi), and superiority measure (p) were calculated based on grain yield and some of yield related traits under normal and heat-stressed conditions. yi, gmp and sti showed the highest correlation with yield under heat stressed condition by 1, 0.93 and 0.92, respectively. gmp, sti, p, and mp had high correlation with yield under both normal and stress conditions on the same direction. correlations between indices based on grain filling duration and peduncle length had the same direction with yield showing importance and effectiveness of these two traits and their indices for detection and screening of high yielding and thermotolerant genotypes under normal and stress conditions.