Molecular breeding for improving drought tolerance in rice mega varieties: progress at IRRI [International Rice Research Inst., Los Baños, Laguna, Philippines]

Drought stress at the reproductive stage is the most devastating. Because of the ongoing process of climate change. the rainfall pattern has become more irregular in the cropping season, causing widespread drought in rice-growing areas, which results in severe yield losses. The development of drought tolerant varieties that maintain good yield under drought is a priority area of rice research for sustainable rice production. Most of the rice mega varieties are high yielding but drought susceptible causing substantial yield losses in the years of severe drought. Marker-assisted breeding(MAB)can be a rapid,precise and an efficient approach to develop high-yielding drought-tolerant rice varieties. At IRRI, several major effect QTLS have been identified in the background of rice mega varieties such as Swarna, IR64,MTU1010 and Vandna from different donors. The main objectives is to introgress and pyramid these QTL2 and enhance the yield by 1.0-1.2 tons per hectare under drought. Some of these QTLS have been already introgressed and pyramided to develop drought tolerant rice mega varieties.Efforts are also made to combine drought and submerge tolerance in Swarna sub1 by MAB. Four major effect QTLs-DTY2.1, DTY2.2, DTY9.1 and DTY12.1 are fine mapped and two other major effect QTLs, QTY3.1 and QTY1.1 are being mapped to make them suitable for MAS. Physiological and molecular mechanisms associated with drought tolerance in some of these QTLs have been studied. Consensus grain yield QTLs and their corresponding orthologs in other cereal crops were identified by comparative genomic approach and QTL validation. In the past few years drought breeding network at IRRI has improved popular rice IR64 and Vandana by MAB and the products are ready for field testing by farmers. The progress of drought molecular breeding work carried out at IRRI is presented.