Identifying novel alleles of rice blast resistance genes Pikh and Pita through allele mining

Abstract

Rice is the staple food for more than half of the world’s population. Demand for rice continues to increase due to the ever-increasing rice consumer base. However, the present rate of increase in rice production (2000-09) has slowed down (1.21%) compared with that of previous decades (1970-90, 2.49%; 1990- 2000, 1.70%) due to various biotic and abiotic stresses (Khush and Jena 2009). Among the biotic stresses, blast, a disease caused by Magnaporthe oryzae, is the most devastating, leading to a 90% yield loss in rice. Although many resistant varieties have already been bred, the breakdown of blast resistance causes yield instability in several rice-growing areas in the world. Of the various strategies tried, enhancement of host-plant resistance is considered one of the important approaches to tackle this disease. Pyramiding of two or more effective resistance genes/alleles into elite cultivars enhances the durability and spectrum of resistance. Hence, identifying superior alleles of effective resistance genes can be immensely helpful in increasing the degree of resistance and can be valuable in breeding durable resistance for blast disease (Ramkumar et al 2010). Of the various blast resistance genes characterized, Pikh and Pita are the two major genes found to confer broad-spectrum resistance to blast in India. With the identification and molecular characterization of Pikh (Madhav et al 2005) and Pita genes (Bryan et al 2000), it is now possible to dissect the naturally occurring allelic variation in these genes from a wide range of germplasm through allele mining. In our study, we used a sequence-based allele mining strategy to isolate novel resistance alleles of Pikh and Pita from landraces and wild Oryza species and studied their effectiveness against blast