Physiological and agronomic characterization of post-flowering heat stress in wild wheat and Robertsonian translocation species

Abstract

Heat stress during flowering and grain-fill stages is a major environmental factor affecting winter wheat production in the Great Plains of the United States. Wild emmer wheat (Triticum diccocoides) is an annual grass species native to the Fertile Crescent and is hypothesized to have a large genetic diversity for improving cultivated wheat. Similarly, Aegilops speltoides is known to possess a higher level of tolerance to abiotic stresses, including heat. The hypothesis is that the chromosomal segment from A. speltoides incorporated into commercial wheat varieties will help enhance heat stress tolerance in winter wheat. The potential of wild wheat species in helping address heat stress damage in cultivated wheat has not been fully explored. Therefore, the major objective of this research project was to capture the genetic variability for post-flowering heat tolerance and asses the physiological and agronomic responses in wild emmer wheat and Robertsonian translocation lines. Chromosomal segments from A. speltoides were incorporated into adapted wheat background, creating Robertsonian translocation lines (RobT’s) (Triticum aestivum-Aegilops speltoides). In the first study, 28 different wild wheat entries were grown under control treatment (25°C) and transferred to high day temperature treatment (35°C) at first signs of flowering and exposed to heat stress for 21 days. Plants exposed to heat stress reached physiological maturity faster, and recorded a significant reduction in yield. Photosynthesis rate and chlorophyll fluorescence were rapidly reduced under heat stress. A moderate range in tolerance to heat stress was identified within the wild wheat with certain accessions having a comparatively higher level of tolerance to heat stress. In the second study a set of 20 RobT’s, along with their parental lines were exposed to heat stress (35°C) at flowering for 21 days. Certain RobT’s outperformed the parent lines, recording a higher photosynthesis rate, maintaining chlorophyll index through an extended period of stress, as well as recording higher yield and lower heat susceptibility index. The findings indicate that the genetic potential in wild wheat, especially RobT’s can be exploited to enhance terminal heat stress in winter wheat. Therefore, wild wheat needs to be explored further and genomic regions inducing greater tolerance to abiotic stresses needs to be incorporated into breeding programs to enhance resilience of popular wheat varieties to current and future warmer climate.