Identification and transfer of beneficial genes for drought tolerance from O. glaberrima to O. sativa

Oryza glaberrima is one of two species of cultivated rice. Grown in Africa, O. glaberrima is also a source of novel genetic material for improvement of cultivated Asian rice, O. sativa. To identify genetic loci for enhancing abiotic stress tolerance, a cross between O. sativa spp. japonica cv. Milyang23 and O. glaberrima was made and 55 BC₃F₇ introgression lines (ILs) with Milyang23 as the recurrent parent have been developed. The O. glaberrima introgressions in these ILs have been characterized using 141 SSR markers and the ILs have been evaluated for physiological traits related to drought stress at the seedling stage. Although both parents exhibited similar responses to the drought stress employed, three ILs (IL9, IL12, and IL54) displayed significantly higher levels of tolerance based on evaluation of fresh and dry weights of shoots and roots. The ILs contain O. glaberrima introgressions in chromosome 1, 3, 7, and 12 that encompass previously reported drought tolerance QTLs, however, SSR analysis indicates that none of the introgressions are common to all three ILs. Restriction enzyme-phased sequencing is being employed to determine if there are additional introgressions not detected by the SSR genotyping. Crosses have been made between Milyang23 and the ILs to develop segregating populations for fine mapping the drought tolerance loci and identifying the underlying genes.