Genetics and genetic improvement of drought resistance in crop plants

Drought limits the agricultural production by preventing the crop plants from expressing their full genetic potential. Three mechanisms, namely drought escape, drought avoidance and drought tolerance are involved in drought resistance. Various morphological, physiological and biochemical characters confer drought resistance. Morphological and physiological characters show different types of inheritance pattern (monogenic and polygenic) and gene action (additive and non-additive), whereas the genes responsible for biosynthesis of different compatible solutes have been identified and cloned from plants, yeast, mouse and human. Different breeding approaches for drought resistance have emerged, with their merits and demerits. Efficient screening techniques are pre-requisite for success in selecting desirable genotype through any breeding programme. Genetic engineering has been successfully applied to identify and transfer different genes responsible for biosynthesis of different metabolites such as proline, trehalose and polyamines from different organisms to crop plants through a targeted approach. Barley hva1 gene responsible for late embryogenesis abundant (LEA) proteins has been transferred to rice to produce drought-resistant transgenics through a shotgun approach. Lack of multidisciplinary approach and precise screening techniques, incomplete knowledge about genetic basis of drought resistance, negative correlation of drought resistance traits with productivity and unavailability of appropriate genes to obtain transgenic plants are the main constraints for genetic improvement of drought resistance. Exploration of wide genetic variation of relevant characters, consideration of more genes at a time to transfer through breeding or genetic engineering method, application of antisense RNA technique, assessment of polypeptides induced under drought and multidisciplinary approach should be included in the future research programmes for drought resistance.