Drought resistance in upland rice, genetic analysis and varietal improvement. Final Technical Report
The purpose was to identify genes for drought resistance and improve varieties of rice for drought-prone uplands by transfer of drought-resistance genes through marker assisted selection. Two upland varieties of rice Azucena and Bala, which differ for root and shoot mechanisms of drought resistance, had been crossed to derive a mapping population in a prior DFID project R4631. These were advanced to produce 205 F6 recombinant inbred lines (RILs). The population was used to make a molecular linkage map with 215 AFLP and RFLP loci. The population was screened for drought-related shoot and root traits in glasshouse and field experiments in multiple locations. Traits measured include root length, thickness and mass, leaf rolling, leaf drying, and relative water content. The RILs were screened for root penetration through wax discs in a collateral project (R6373) and a QTL map for root penetration through wax was published (Price et al., 1999a). Preliminary QTL maps were made for drought response traits and root characteristics (Price et al., 1999b). The population was also screened for resistance to the fungal pathogen blast. The project has identified molecular markers at loci which are theoretically influencing drought resistance in rice, and has confirmed the location of some of the more notable QTLs through comparisons with other studies. Rooting ability QTLs have been shown to influence shoot responses to drought, because some drought response QTLs map in similar regions. Five Indian upland rice varieties were screened with RFLP markers for polymorphism. Kalinga III was selected for root-trait improvement by marker assisted selection (MAS). Kalinga III is popular in drought-prone areas of India but it has poor rooting ability. Four root growth QTLs were identified as targets for transfer to Kalinga III from Azucena on chromosomes 2,7,9 and 11. A gene for aroma in Azucena on chromosome 8 was also targeted for transfer. Backcrossing and MAS has resulted in BC3 lines which contain the target loci. Segregating lines from the BC2 generation with Azucnea alleles at 1-3 root QTLs have been disseminated to breeders in India. These lines may have an increased ability to withstand drought and they are available for farmers to select in participatory plant breeding programmes in India and Nepal.