The Independent and Combined Effects of Drought and High Temperature Stress On Physiological, Growth and Yield Traits of Synthetic Wheat.

Drought and high temperature (HT) mostly occur simultaneously, but little has been explored to understand their combined effects on performance of crop. This experiment was conducted to identify synthetic wheat lines having tolerance to combined stress of drought and HT at reproductive stage. The second objective was to quantify the independent and combined effects of drought and HT on physiological, growth and yield traits of wheat. Four hexaploid synthetic wheat lines (Altar 84 / Aegilops tauschii; Altar 84 / AO'S'; GR'S' / BOY'S'; and GAN / Aegilops tauschii) and two bread wheat cultivars (Halberd and Dharwar Dry) were evaluated at controlled environmental conditions: (a) Control: 25/19°C (day/nighttime) / full irrigation; (b) Drought: 25/19°C (day/nighttime) / withholding water; (c) HT: 36/30°C (day/nighttime) / full irrigation; and (d) Combined: 36/30°C (day/nighttime) / withholding water. The stress was imposed for 16 days from flowering stage (Feeks 10.5.1). Overall, across all genotypes, drought decreased grain number per panicle, individual kernel weight, grain yield per plant (YLD) and harvest index by 7, 40, 71 and 59%; HT decreased them by 21, 66, 82 and 75%; and combined stress caused a decline by 46, 83, 92 and 88% respectively. The effect of drought on YLD was least in Altar 84 / AO’S’ and GR’S’ / BOY’S’ (below 60% decline from control) as compared to others (>69% decline). Altar 84 / AO’S’ showed significant tolerant to HT (66% decline) followed by halberd (69% decline). Altar 84 / AO’S’ had also least decline in YLD under combined stress (about 81%) as compared to others (>than 89%). Under combined stress, the GAN / Aegilops tauschii had up to 99.8% yield reduction. These results show that the combined effect of drought and high temperature is more detrimental and hexaploid synthetic wheat line Altar 84 / AO'S' can be utilized for improving stress tolerance in wheat.