Identification and introgression of novel bacterial blight resistance from Oryza glaberrima Steud

Abstract

Background: Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the major diseases affecting rice production in India and globally. Developing resistant cultivar is generally regarded as the most effective and economical means of controlling this dreaded disease.Results: A total of 31 accessions of O. glaberrima were screened for BB resistance consecutively for four seasons and 28 accessions consistently exhibited high level of resistance with a mean lesion length of < 3cm. Molecular characterization using gene specific markers revealed absence of major resistance genes viz., xa5, xa13, Xa21, Xa38, xa41(t) and xa45 in these accessions, indicating the possibility of presence of novel gene(s) conferring BB resistance. In order to transfer BB resistance from O. glaberrima, resistant accessions EC861812 showing high level of BB resistance was crossed to the susceptible rice cultivar, IR64 and resultant interspecific hybrid plants were further backcrossed to IR64. Backcrossing was done up to BC2 generation and during each generation of backcrossing, the plants were evaluated for their BB reaction to identify BB resistant ones. High level of spikelet sterility was observed in F1 and subsequent backcross generations. BB reactions pattern in F1 and BC1F2 indicated single dominant gene conferring BB resistance in EC861812. We identified six resistant plants at BC2F2 (with mean lesion length of 0.1-0.8 cm) which were genotyped with 70 parental polymorphic SSR markers. The recovery of recurrent parent genome among the six resistant lines was found to be 65.1 to 84.5% with average of 67.5%. Interestingly, analysis of BC2F2 population for yield attributing traits showed transgressive segregation for plant height, productive tillers, panicle length which indicates that O. glaberrima also harbor beneficial alleles for yield related traits. Conclusion: BB resistant introgression lines derived from O. glaberrima identified in the present study will serve as precious pre-breeding resources for development of durable BB resistant elite breeding varieties.