Field crops and the fear of heat stress—Opportunities, challenges and future directions
The increased probability of occurrence of more intense and frequent heat stress episodes and extended warmer nights in the future are major challenges towards sustaining agricultural production. Cereals, millets and oil seed crops respond differently to increasing temperature at different growth and developmental stages but are highly susceptible to heat stress during the gametogenesis and the flowering stages. Interestingly, the duration of stress exposure induces differential responses i.e. season-long exposure to hightemperature and short episodes of heat stress coinciding with reproductive processes. Season-long high-temperature stress decreased biomass production, seed number, individual seed weight and yield of all grain crops. Short duration heat stress coinciding with either gametogenesis or anthesis leads to negative impact of seed-set, while stress exposure at post-anthesis stages decreased seed filling duration leading to decreased seed weight. Based on extensive research we have identified temperature thresholds across field crops and quantified the above changes. Impact of heat stress on pollen production, pollen viability, pollen lipid profiles, alternations in the pollen and stigmatic surface, pollen reactive oxygen species production, their membrane damage etc., differentiating contrasting cultivars across different field crops will be highlighted. In addition, considering the differential rate of increase in minimum night temperature, different physiological routes inducing yield losses under high day and high night temperature will be presented. Genetic variability across field crops in response to heat stress and more interestingly options from wild species of wheat (higher heat tolerance at flowering), rice (heat escape through early morning flowering) and their usefulness in heat stress tolerance breeding will be an interesting addition to our talk. The current progress achieved, opportunities available, unaddressed challenges and future direction of research that could help in crop improvement to sustain global food production under future hotter climates will be discussed.