Effects of drought and/or high temperature stress on wild wheat relatives (AEGILOPS species) and synthetic wheats.

Abstract

High temperature (HT) and drought are detrimental to crop productivity, but there is limited variability for these traits among wheat ([italics]Triticum aestivum[end italics] L.) cultivars. Five [italics]Aegilops[end italics] species were screened to identify HT (52 accessions) and drought (31 accessions) tolerant species/accessions and ascertaining traits associated with tolerance. Four synthetic wheats were studied to quantify independent and combined effects of HT and drought. [italics]Aegilops[end italics] species were grown at 25/19°C day/night and 18 h photoperiod. At anthesis, HT was imposed by transferring plants to growth chambers set at 36/30°C, whereas in another experiment, drought was imposed by withholding irrigation. Synthetic wheats were grown at 21/15°C day/night and 18 h photoperiod. At anthesis or 21 d after anthesis, plants were exposed to optimum condition (irrigation + 21/15°C), HT (irrigation + 36/30°C), drought (withhold irrigation + 21/15°C), and combined stress (withhold irrigation + 36/30°C). Stresses were imposed for 16 d. High temperature and drought stress significantly decreased chlorophyll, grain number, individual grain weight, and grain yield of [italics]Aegilops[end italics] species (≥ 25%). Based on a decrease in grain yield, [italics]A. speltoides[end italics] and [italics]A. geniculata[end italics] were most tolerant (~ 61% decline), and [italics]A. longissima[end italics] was highly susceptible to HT stress (84% decline). Similarly, [italics]A. geniculata[end italics] had greater tolerance to drought (48% decline) as compared to other species (≥ 73% decline). Tolerance was associated with higher grains spike [superscript]-1 and/or heavier grains. Within [italics]A. speltoides[end italics], accession TA 2348 was most tolerant to HT with 13.5% yield decline and a heat susceptibility index (HSI) 0.23. Among [italics]A. geniculata[end italics], TA 2899 and TA 1819 were moderately tolerant to HT with an HSI 0.80. TA 10437 of [italics]A. geniculata[end italics] was the most drought tolerant accession with 7% yield decline and drought susceptibility index 0.14. Irrespective of the time of stress, HT, drought, and combined stress decreased both individual grain weight and grain yield of synthetic wheats by ≥ 37%, 26%, and 50%, respectively. These studies suggest a presence of genetic variability among [italics]Aegilops[end italics] species that can be utilized in breeding wheat for HT and drought tolerance at anthesis; and combined stress of drought and high temperature on synthetic wheats are hypo-additive in nature.