Abstract
Wheat is sensitive to high-temperature stress with crop development significantly impaired depending on the severity and timing of stress. Various physiological mechanisms have been identified as selection targets for heat tolerance; however, the complex nature of the trait and high genotype × temperature interaction limits the selection process. A three-tiered phenotyping strategy was used to overcome this limitation by using wheat genotypes developed from the ancient domesticated wheat, emmer (Triticum dicoccon Schrank), which was considered to have a wide variation for abiotic stress tolerance. A contrasting pair of emmer-based hexaploid lines (classified as tolerant; G1 and susceptible; G2) developed from a backcross to the same recurrent hexaploid parent was chosen based on heat stress responses in the field and was evaluated under controlled glasshouse conditions. The same pair of contrasting genotypes was also subsequently exposed to a short period of elevated temperature (4 days) at anthesis under field conditions using in-field temperature-controlled chambers. The glasshouse and field-based heat chambers produced comparable results. G1 was consistently better adapted to both extended and short periods of heat stress through slow leaf senescence under heat stress, which extended the grain filling period, increased photosynthetic capacity, increased grain filling rates, and resulted in greater kernel weight and higher yield. The use of a combination of phenotyping methods was effective in identifying heat tolerant materials and the mechanisms involved.
Highlights
High temperature is a constraint to the sustainable production of wheat in major wheat growing areas of the world (Asseng et al, 2015)
The temperature and humidity inside the heat chambers, both FCT1 and FCT2, during the 4 days of treatment are given in Supplementary Figure 3, where plants under FCT2 experienced higher temperature conditions
The contrasting performance of the pair of related emmerderived lines at high temperature indicated that heat stress tolerance was under genetic control, which should be further studied
Summary
High temperature is a constraint to the sustainable production of wheat in major wheat growing areas of the world (Asseng et al, 2015). Grain size is reduced due to a shorter duration of the grain filling period and early senescence (Shirdelmoghanloo et al, 2016a), whereas grain quality decreases (Nuttall et al, 2017; Ullah et al, 2020a) and the percentage of Physological Basis of Heat Tolerance shriveled/broken grain ( called screenings) increases (Farooq et al, 2011; Ferreira et al, 2012; Nuttall et al, 2017). Heat waves and higher average day/night temperatures are increasing with climate change; mitigation strategies are needed to stabilize grain yield and quality (Prasad and Djanaguiraman, 2014; García et al, 2015). Non-destructive methods, such as the measurement of canopy greenness using the normalized difference vegetation index (NDVI) and optically derived chlorophyll content, have been used to rapidly phenotype stay-green in the field (Lopes and Reynolds, 2012; Christopher et al, 2014; Talukder et al, 2014); stay-green has relatively low heritability, which has limited its adoption in breeding programs
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