Evaluation of heat stress tolerance in irrigated environment of T. aestivum and related species. I. Stability in yield and yield components

Wheat production is often limited by continual or terminal heat stress. The current study was aimed at the characterization of wild relatives and cultivated Triticum species for their heat tolerance in yield and its analysis in relation to yield components which confer yield stability at the three ploidy levels. Thirty-two non-cultivated and cultivated genotypes belonging to diploid, tetraploid and hexaploid wheat species were evaluated for heat stress tolerance in the field under full irrigation. Wheat species were sown in the field(New Delhi, India; 77°12′E, 28°40′N, 228.6 m m.s.l) at two dates of sowing, November (normal) and January (late Sowing) during winter seasons of 1994–95 and 1995–96. The late sown crop experienced 3°C warmer temperatures than that of the normal sown crop. Wide variability was observed for grain yield stability under heat stress, as the heat susceptibility index (S) ranged from 0.13 to 2.08. Hexaploidy conferred the productive and adaptive advantages as it combined high yield and stability when compared to the tetraploid and diploid groups. However within each ploidy group wide variation was observed for heat tolerance. T. aestivum cv C306 & HI1136, T. dicoccoides, T. monococcum acc. BSP1 and Ae. speltoides ssp. liqustica were highly heat tolerant in their grain yield. Stability in grain no. m- 2 conferred yield stability in all three ploidy levels, although grain weight stability also contributed to yield stability in moderately stable T. turgidum and T. sphaerococcum under heat stress. Higher biomass and grain no. m-2 are the two important traits which could be considered potential selection criteria for yield under heat stress. Of the two components of grain no. m-2, stability in spike no. m-2could be considered more important trait than grain no. spike-1. Since wide variation for heat tolerance of all the yield components are available among the wheat species, these species can be used for improving specific yield components of cultivated wheat. This revised version was published online in July 2006 with corrections to the Cover Date.