Marker Assisted Breeding For Development Of Bacterial Blight Resistant Rice

Abstract

Bacterial blight (BB) disease caused by the pathogen Xanthomonas oryzae pv oryzae (Xoo) limits rice yields in all major rice‐growing regions of the world including India, especially in the highly productive irrigated lowlands and rainfed areas. Since chemical control of the pathogen is not very effective, deployment of host plant resistance is the most preferred strategy for management of the disease. Till date, more than 30 genes conferring resistance to various races of the pathogen have been identified and many of these like Xa1, Xa4, xa5, Xa7, xa8, xa13, Xa21 and Xa27 have been tagged and mapped with the help of molecular markers. Some of these like Xa4, xa5, Xa7 and xa13 have been utilized in breeding resistant rice varieties as single genes. Large‐scale and long‐term cultivation of varieties carrying a single resistance gene may result in a significant shift in pathogen race frequency with consequent breakdown of resistance in cultivars carrying single resistance genes. In order to overcome this problem, pyramiding of two or more major resistance genes into a single varietal background is recommended. Gene‐ pyramiding process can be facilitated and accelerated through the deployment of molecular markers linked to the resistance genes. Through marker‐assisted gene pyramiding, many bacterial blight resistant cultivars have been developed and some of these have been commercially released. This article reviews the research developments related to identification of various bacterial blight resistance genes, their molecular mapping, characterization and development of bacterial blight resistant rice varieties and hybrids through conventional and marker‐assisted breeding from an Indian perspective.