Genetics and Genomics of Bacterial Blight Resistance in Rice

Abstract

Rice is an important food crop for half the world's population and has been in cultivation for over 10,000 years. During the last few decades, rice has evolved intricate relationships with associated pathogens and pests, bacterial blight (BB) being one of the most important among them. Utilization of resistant varieties with agricultural management practices is a more effective way to control BB. Of the 42 different resistance (R) genes identified to confer BB resistance, 9 have been isolated and cloned, whereas a few of the avirulence genes and a large number of candidate pathogenicity genes have been isolated from Xanthomonas oryzae pv. oryzae. The complete genome sequences of two different rice subspecies japonica and indica and three different races of BB pathogen are available. Therefore, the interaction between rice-Xoo could be deciphered and pave a way to study the molecular aspects of bacterial pathogenesis and host counter measures like innate immunity and R gene-mediated immunity. Although several of the type III effectors of Xoo have been characterized and the host targets of a few of them identified, a relatively large number of candidate effectors remain to be studied and their functional analysis may provide key for developing broad spectrum and durable resistance to BB.

Marker-assisted selection and gene pyramiding for resistance to bacterial leaf blight disease of rice (Oryza sativaL.)

“…Plants usually contain a single locus which confers resistance against a complementary avirulence. This has been shown from genetic analysis of many plant pathogen interactions [10]. Japan, IRRI, Sri Lanka, India and China were among the first to study the inheritance of BLB resistance in rice.…”

“…Substantial attempt has been made to identify genes responsible for pathogenesis of Xoo and roles of each gene in causing disease. The genome sequence of Xoo strains like KACC10331, MAFF311018 and PXO99A has made the knowledge of pathogenesis genes clearer [10].…”

“…Researchers found it difficult to characterize and differentiate the R-genes due to diversity of Xoo strains in various countries. The identical differential standard was set up to compare the genes identified [10]. Currently, 42 BLB R-genes have been discovered in rice [10][11][12].…”

“…The identical differential standard was set up to compare the genes identified [10]. Currently, 42 BLB R-genes have been discovered in rice [10][11][12]. These genes were identified from mutant populations, cultivated and wild rice species and confer resistance against different Xoo strains ( Table 1).…”

“…Initial effort to map microsatellites in rice was made by Zhao and Kochert [78] using (GGC)n, followed by mapping of (GA/AG)n, (ATC) 10 and (ATT) 14 microsatellites by Panaud et al [80]. Presently, over 20,000 SSR markers (microsatellites), which are well distributed landmarks all over the genome of rice, have been developed [68,[81][82][83].…”