Field crops and the fear of heat stress—Opportunities, challenges and future directions

Abstract

Predicted increase in temperature variability can result in short duration of heat stress episodes coinciding with vulnerable reproductive processes leading to significant reduction in floretfertility in crops. Recent knowledge on alternations in the pollen and stigmatic morphology, pollen biochemical and lipid composition, variable sensitivity of floral reproductive organs and differential temperature thresholds across crops advances the knowledge on heat stress induced reduction in seed-set and harvest index. Rapid increase in night-time temperature, leading to narrowing diurnal temperature amplitude is a major emerging threat to sustain crop productivity. Interestingly, wild wheat (Aegilops spp.) with higher heat-tolerance and wild rice (Oryza officinalis) escaping damage by completing flowering during early morning hours, are examples of novel opportunities to breed field crops resilient to heat stress. Information on mechanisms leading to heat stress induced sterility is biased towards rice, wheat and sorghum, while the same across other field crops is limited. Hence, increasing research efforts in this direction is critical and timely.

Identification of High-Temperature Tolerant Lentil (Lens culinaris Medik.) Genotypes through Leaf and Pollen Traits

“…These reports are matching some previous findings on chickpea (Kumar et al, 2013) and mungbean (Kaur et al, 2015). Our results indicated that the leaves of LS plants under heat stress were adversely affected and responded by increasing their temperature, reducing leaf water status and inhibiting stomatal conductance, which agrees with previous reports on other crops (Prasad et al, 2017). Heat stress results in decrease in water content of the cells, reducing cell size and, in due course, restricting plant growth (Rodriguez et al, 2005; Sharma et al, 2016).…”

Thresholds, sensitive stages and genetic variability of finger millet to high temperature stress

“…(), loss of pollen viability under HT stress is associated with altered carbohydrate metabolism and starch deficiency in developing pollen grains. Other mechanism associated with loss of viability of gametes includes increased production of reactive oxygen species, alterations in lipid composition, anatomical abnormalities and decreased antioxidants (Prasad et al., ).…”

“…R.Br. ), dry bean ( Phaseolus vulgaris L.), peanut ( Arachis hypogea L.) and soybean ( Glycine max L.) (reviewed in Prasad et al., ). However, little information is available on effect of HT stress on finger millet yield and its components.…”

“…Research on various cereals revealed that HT stress decreased chlorophyll content, photosystem II quantum yield, photosynthetic rate and economic yield (Djanaguiraman, Prasad, Murugan, Perumal, & Umesh, ; Narayanan, Prasad, Fritz, Boyle, & Gill, ; Sunoj, Shroyer, Jagadish, & Prasad, ). Studies on rice, wheat, maize ( Zea mays L.), sorghum, pearl millet, peanut, cowpea ( Vigna unguiculata L.) and common bean indicated that reproductive stage appears to be more vulnerable to HT than vegetative stages of crop development (reviewed in Hatfield et al., , ; Prasad & Djanaguiraman, ; Prasad et al., ). Studies on maize (Schoper, Lambert, Vasilas, & Westgate, ), wheat (Ferris, Ellis, Wheeler, & Hadley, ; Prasad, Pisipati, Ristic, Bukovnik, & Fritz, ), rice (Matsui, Omasa, & Horie, ; Prasad, Boote, Allen, Sheehy, & Thomas, ; Prasad et al., ) and sorghum (Djanaguiraman et al., ; Prasad, Djanaguiraman, Perumal, & Ciampitti, ) indicated that HT stress during reproductive stages decreased the number of seeds per panicle and individual seed weight, resulting in lower grain yields.…”

“…Genetic diversity among germplasm with varied degree of HT stress tolerance has been well documented in cereals such as rice, wheat, sorghum and pearl millet (Djanaguiraman et al., , ; Nguyen et al., ; Pradhan, Prasad, Fritz, Kirkham, & Gill, ; Prasad, Boote, Allen, Sheehy et al., ). In cereals, the HT‐tolerant genotypes are defined by maintenance of photosynthesis, chlorophyll content and stomatal conductance under HT stress, while the yield of these genotypes is maintained through higher seed set, grain number and individual grain weight at HT (Djanaguiraman et al., , ; Nguyen et al., ; Pradhan et al., ; Prasad, Boote, Allen, Sheehy et al., ; Prasad et al., ; Singh et al., ; Yang, Sears, Gill, & Paulsen, ). However, research on quantifying genetic variability for HT stress in finger millet is limited.…”