Genotypic Differences in Effects of Short Episodes of High‐Temperature Stress during Reproductive Development in Sorghum

Abstract

Recent studies on sorghum [Sorghum bicolor (L) Moench] showed that episodes of high‐temperature stress around anthesis could adversely affect grain yield via effects on pollen germination with varying responses among genotypes. The objectives of this study were to determine the reproductive development phase most sensitive to heat stress and to determine whether genotypic differences in high‐temperature tolerance were associated with differences in either cardinal temperatures for pollen germination, the duration of the period of sensitivity to high temperatures, or the extent of the response to high temperature per se. To determine cardinal temperatures, pollen from six genotypes, differing in high‐temperature tolerance, was incubated on a gradient plate at temperatures between 10 and 40°C. To identify the critical period of high temperature sensitivity, plants of two genotypes with contrasting high‐temperature tolerance were grown under optimum (31 vs. 21°C) and high (38 vs. 21°C) day vs. night temperatures, with selected plants reciprocally transferred between the two temperatures for 5‐d periods from just before flag leaf full expansion until 20 d thereafter. Pollen germination, seed set, and grain yield were most sensitive to high temperatures immediately around anthesis. Effects on seed mass were smaller and independent of seed set. Genotypes differed in the magnitude of the response to high temperatures, rather than in the duration of the critical period, and the adverse effect of high temperatures increased with duration of exposure during this critical period. These differences were not associated with cardinal temperatures for pollen germination. These results could assist in identifying selection targets for crop improvement programs.

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

“…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.…”

High Temperature Effects on in vitro Pollen Germination and Seed Set in Field Pea

“…In vitro pollen germination has been used to screen heat tolerance in many crops (Kakani et al 2002(Kakani et al , 2005Salem et al 2007;Devasirvatham et al 2012;Song et al 2015;Singh et al 2015Singh et al , 2016. On the other hand, Petkova et al (2009) suggested that to assess heat-tolerant cultivars of field pea, in vitro pollen-tube length is more reliable than pollen germination percentage because successful fertilization depends on whether pollen tubes actually reach the ovules.…”

“…Cardinal temperatures (T min , T opt , and T max ) for in vitro pollen germination in cotton were 15.0, 31.8, and 43.3°C, respectively (Kakani et al 2005), whereas in groundnut, they were identified as 14.1, 34.4, and 43.0°C (Kakani et al 2002). In sorghum, the maximum temperature for in vitro pollen germination is 43.2°C (Singh et al 2016). In field pea, in vitro pollen germination and pollen-tube length decreased with an increase in temperature from 24 to 36°C (Jiang et al 2015).…”

“…Indeed, with 64-72% of genes in vegetative tissues of Tradescantia and maize also being expressed in pollen (reviewed by Hamilton and Mascarenhas, 1997), in vitro pollen germination has been investigated as a rapid screening criterion for tolerance to a variety of agronomically-important characteristics including soil acidity and salinity, metal and herbicide toxicity, as well as for heat tolerance (Sari-Gorla and Frova, 1997). Exposure to high temperatures reduces in vitro pollen germination percentage and pollen-tube length in many crops including canola (Singh et al 2008;Morrison et al 2016), cotton (Kakani et al 2005Song et al 2015), and sorghum (Nguyen et al 2013;Djanaguiraman et al 2014;Singh et al 2015Singh et al , 2016, as well as legumes like chickpea (Cicer arietinum; Devasirvatham et al 2012), field pea (Pisum sativum; Petkova et al 2009;Lahlali et al 2014;Jiang et al 2015), groundnut (Arachis hypogaea; Kakani et al 2002), and soybean (Glycine max; Koti et al 2005;Salem et al 2007). In sorghum, seed-set percentage (the number of seeds filled at physiological maturity divided by the total number of florets) was strongly and positively associated with in vitro pollen germination across genotypes and temperature regimes (Nguyen et al 2013;Singh et al 2015Singh et al , 2016.…”