Effects of drought and high temperature stress on synthetic hexaploid wheat.

Drought and high temperature often occurs simultaneously, causing significant yield losses in wheat (Triticum aestivum L.). The objectives of this study were to: (i) quantify independent and combined effects of drought and high temperature stress on synthetic hexaploid wheat genotypes at anthesis and at 21 days after anthesis; and (ii) determine whether responses to stress varied among genotypes. Four synthetic hexaploid and two spring wheat genotypes were grown from emergence to anthesis (Experiment I) and emergence to 21 days after anthesis (Experiment II), with full irrigation and 21/15°C day/night temperature. Thereafter, four treatments were imposed for 16 days as (a) optimum condition: irrigation+21/15°C, (b) drought stress: withhold irrigation+21/15°C, (c) high temperature stress: irrigation+36/30°C and (d) combined stress: withhold irrigation+36/30°C. Results indicated a decrease in leaf chlorophyll, individual grain weight and grain yield in an increasing magnitude of drought<high temperature<combined stress. There were 69, 81 and 92% grain yield decreases in Experiment I and 26, 37 and 50% in Experiment II under drought, high temperature and combined stress respectively. Synthetic hexaploid wheat genotypes varied in their response to stresses. Genotypes ALTAR 84/AO'S' and ALTAR 84/Aegilops tauschii Coss. (WX 193) were least affected by combined stress in Experiments I and II respectively. Overall, combined effect of drought+high temperature stress was more detrimental than the individual stress and the interaction effect was hypo-additive in nature.