Resilience of Pollen and Post‐Flowering Response in Diverse Sorghum Genotypes Exposed to Heat Stress under Field Conditions

Abstract

The predicted increase in global temperatures will increase the probability of exposing sorghum [Sorghum bicolor (L.) Moench] to heat stress during critical reproductive developmental stages, such as flowering and post‐flowering periods. Greenhouse and field studies were conducted to quantify the impact of heat stress on pollen germination and other post‐flowering physiological processes affecting grain yield. Pollen collected from 24 diverse sorghum genotypes grown under greenhouse conditions were tested for their tolerance to heat stress. Using the same set of genotypes, field‐based heat tents were used to impose heat stress from booting stage to maturity. Pollen grains from field experiments were tested under three different types of heat stress combinations to identify genotypes with pollen having true heat tolerance. Heat stress induced a significant reduction in grain yield (16–73%), pollen germination (2–95%), photosynthesis (0.5–50%), and photochemical efficiency of photosystem II (1–8%) and increased thylakoid membrane damage (2–27%) compared with control conditions. Reduced grain yield with heat stress exposure was not compensated by grain weight increase. In vitro pollen germination revealed SC155 to possess true heat‐tolerant pollen, even under severe stress exposure. Macia and BTx378 recorded higher relative grain yield and pollen germination, providing opportunities for mapping genomic regions responsible for heat tolerance using currently available biparental mapping populations in RTx430 and BTx623 backgrounds, respectively.

Disaggregating sorghum yield reductions under warming scenarios exposes narrow genetic diversity in US breeding programs

“…Although sorghum is known to be highly heat-tolerant, it is prone to yield losses during the flowering and/or postflowering phases (12,13,27). Sorghum's response to heat stress has been primarily quantified by imposing stress at predetermined stages using highly controlled environment facilities or field-based tents (8)(9)(10)(11)(12)(13)27) involving few cultivars.…”

“…Sorghum's response to heat stress has been primarily quantified by imposing stress at predetermined stages using highly controlled environment facilities or field-based tents (8)(9)(10)(11)(12)(13)27) involving few cultivars. These findings under controlled conditions limit our ability to develop robust conclusions regarding sorghum's heat-stress sensitivity (28).…”

“…Both controlled-environment studies (8)(9)(10)(11) and more recent studies using custom-designed field-based structures (12,13) have documented the susceptibility of sorghum to heat stress during the critical flowering and grain-filling stages. Hence, most empirical studies and current breeding efforts have been aimed toward reducing yield losses with stress coinciding with the sensitive flowering and grain-filling stages.…”

Quantifying the Impact of Heat Stress on Pollen Germination, Seed Set, and Grain Filling in Spring Wheat

“…Wheat has different optimum temperatures for both vegetative and reproductive stages, which vary between species and genotypes (Farooq et al, 2011). Pollen viability is a major determinant of reproductive success, and its genetic variability under heat stress exposure has been documented in rice (Oryza sativa L.; Coast et al, 2016), sorghum [Sorghum bicolor (L.) Moench; Sunoj et al, 2017], peanut (Arachis hypogaea L.; Kakani et al, 2002), and soybean [Glycine max (L.) Merr. Pollen viability is a major determinant of reproductive success, and its genetic variability under heat stress exposure has been documented in rice (Oryza sativa L.; Coast et al, 2016), sorghum [Sorghum bicolor (L.) Moench; Sunoj et al, 2017], peanut (Arachis hypogaea L.; Kakani et al, 2002), and soybean [Glycine max (L.) Merr.…”

Deterioration of ovary plays a key role in heat stress‐induced spikelet sterility in sorghum

“…However, a substantial increase in temperature variability around the mean is a significant new dimension that most crops are not programmed to cope with. This increase in variability will lead to more intense but short episodes of heat stress, which, when coincided with a critical reproductive stage such as flowering, leads to significant reduction in yield and productivity of field crops (maize [ Zea mays L.], Siebers et al, ; rice [ Oryza sativa L.], Jagadish et al, ; sorghum [ Sorghum bicolor [L.] Moench], Sunoj et al, ; and wheat [ Triticum aestivum L.], Aiqing et al, ; Bheemanahalli et al, ). Even under current environmental conditions, heat stress coinciding with reproductive stages has resulted in significant economic losses in field crops grown in different geographical locations (rice [Ishimaru et al, ]; sorghum [Tack, Lingenfelser, & Jagadish, ]; wheat [Tack, Barkley, & Nalley, ]).…”