Mapping quantitative trait loci and marker assisted selection for the improvement of drought tolerance in rice

Abstract

Drought stress is a major constraint to rice production especially in rainfed ecosystems. The development of drought tolerant rice cultivars through conventional breeding has met with little success. The complexity of drought tolerance mechanism(s) and the difficulty in incorporation of physiological selection criteria in breeding programmes are important reasons for this lack of progress. Deep and thick roots enable rice plants to access deep soil moisture and help to avoid drought. Capacity for osmotic adjustment (OA) helps to maintain turgor under water stress and sustains growth under declining soil moisture. Both root traits and OA are difficult to phenotype in large segregating progenies. Quantitative trait loci (QTL) mapping combined with marker-assisted selection (MAS) approach offers a tool for indirect selection of complex traits such as drought tolerance. Molecular markers linked to various root traits and OA have been mapped in rice. Consistent QTL linked to root traits and OA have been identified thus enabling MAS of these traits. However, the value of these QTL have to be tested under field conditions in the target ecosystems using near isogenic lines. QTL linked to field drought tolerance in terms of grain yield under stress have been mapped recently. QTL for root traits overlapped with QTL for drought tolerance in the field. Identification and introgression of such QTL into high yielding elite cultivars will lead to increase in rice production in drought- prone rainfed ecosystems. Drought stress is a major constraint to rice production especially in rainfed ecosystems. The development of drought tolerant rice cultivars through conventional breeding has met with little success. The complexity of drought tolerance mechanism(s) and the difficulty in incorporation of physiological selection criteria in breeding programmes are important reasons for this lack of progress. Deep and thick roots enable rice plants to access deep soil moisture and help to avoid drought. Capacity for osmotic adjustment (OA) helps to maintain turgor under water stress and sustains growth under declining soil moisture. Both root traits and OA are difficult to phenotype in large segregating progenies. Quantitative trait loci (QTL) mapping combined with marker-assisted selection (MAS) approach offers a tool for indirect selection of complex traits such as drought tolerance. Molecular markers linked to various root traits and OA have been mapped in rice. Consistent QTL linked to root traits and OA have been identified thus enabling MAS of these traits. However, the value of these QTL have to be tested under field conditions in the target ecosystems using near isogenic lines. QTL linked to field drought tolerance in terms of grain yield under stress have been mapped recently. QTL for root traits overlapped with QTL for drought tolerance in the field. Identification and introgression of such QTL into high yielding elite cultivars will lead to increase in rice production in drought- prone rainfed ecosystems.