High Temperature Tolerance In Aegilops Species and Its Potential Transfer to Wheat.

High temperature (HT) stress is highly detrimental to crop productivity but there is limited variability for this trait among wheat cultivars. The objectives of this research were to screen wild wheats (Aegilops species) for tolerance to HT stress at the reproductive stage; and to measure physiological, and yield traits associated with the tolerance. Fifty-two accessions belonging to five Aegilops species were evaluated at optimum temperature (OT, 25/19°C day/night) and HT (36/30°C), with a photoperiod of 18 h. Stress was imposed at anthesis and continued for 16 d. Across species, HT decreased chlorophyll, grain number spike^-1, individual grain weight and grain yield plant^-1 by 38%, 40%, 56%, and 70%, respectively. Based on decrease in grain yield, A. speltoides Tausch and A. geniculata Roth were most tolerant, and  A. longissima Schweinf. & Muschl. was highly susceptible to HT stress. Tolerance was associated with high grain number spike^-1 and/or individual grain weight. Within A. speltoides, accession TA 2348 was highly tolerant to HT with 13.5% decline in grain yield and a heat susceptibility index (HSI) 0.23, whereas TA 1787 and TA 2097 were highly susceptible with > 82% yield decline and HSIs > 1.4. Among A. geniculata, two moderately HT tolerant accessions TA 2899 and TA 1819 were identified, with an HSI of 0.80. Our results suggest that there is genetic variability among Aegilops species that can be utilized in breeding programs for improving HT tolerance in wheat at reproductive stage.