Effect of heat and drought under crops in rainfed/marginal environments and mitigation strategies through breeding for tolerance: A review

Significant crop yield losses in agricultural crops are caused by abiotic stresses and under field conditions, the moisture and heat stress prevalent together. The combination of heat and drought stresses exhibit detrimental effect on the productivity of crops compared with each of the stresses applied individually. These two stresses induce biochemical, molecular and physiological changes and responses that influence the whole plant process affecting crop phenology, reproduction, flowering, anthesis/pollen viability, pollination/fertilization, length of grain filling duration, grain setting, grain size, grain yield and ultimately grain quality. Breeding crop plants for tolerance against heat and drought for target environment is of paramount importance. For this purpose, various eco-morphophysiological traits need to be considered along with the efficient screening procedures. Similarly, other important traits like efficient root system, stay green character and harvest index are considered useful for breeding programmes against moisture and heat stresses. Additionally, marker assisted selection (MAS), quantitative traits loci (QTLs) and genomics have big role to play for enhancing efficiency, time saving, accuracy and greater degree of precision. The fast delivery of heat and drought tolerant varieties can be made through participatory seed production programme. Presently, genetically modified (GM) crops with respect to heat and drought tolerance have not proved as thought initially, and a combination of conventional, MAS and transgenic would be the better option. Nevertheless, the partnerships at various levels to develop cultivars with tolerance to these stresses will be crucial. The status of crop productivity in marginal environments in India along with combined effect of heat and drought stresses have been reviewed and breeding approaches including strengthening of local seed system under marginal conditions has also been detailed.