Bacterial leaf blight resistance in rice: a review of conventional breeding to molecular approach

Abstract

Breeding for disease resistant varieties remains very effective and economical in controlling the bacterial leaf blight (BLB) of rice. Breeders have played a major role in developing resistant rice varieties against the BLB infection which has been adjudged to be a major disease causing significant yield reduction in rice. It would be difficult to select rice crops with multiple genes of resistance using the conventional approach alone. This is due to masking effect of genes including epistasis. In addition, conventional breeding takes a lot of time before a gene of interest can be introgressed. Linkage drag is also a major challenge in conventional approach. Molecular breeding involving markers has facilitated the characterization and introgression of BLB disease resistance genes. Biotechnology has brought another innovation in form of genetic engineering (transgenesis) of rice. Although, molecular breeding cannot be taken as a substitute for conventional breeding, molecular approach for combating BLB disease in rice is worthwhile given the demand for increased production of rice in a fast growing population of our society. This present article highlights the recent progress from conventional to molecular approach in breeding for BLB disease resistant rice varieties.

Marker-assisted introgression of multiple resistance genes confers broad spectrum resistance against bacterial leaf blight and blast diseases in Putra-1 rice variety

“…The donor parent IRBB60 which contains four BLB R-genes Xa4, xa5, xa13 and Xa21 [6] was collected from the International Rice Research Institute (IRRI), the Philippines. Xa4 and Xa21 are the dominant genes while xa5 and xa13 are in the recessive condition.…”

“…To date, 42 Xoo resistance genes have been identified in rice and some of them have been incorporated into new varieties [5]. Generally, the disease is favoured by temperatures at 25 to 34°C, with relative humidity more than 70% and most rice growing regions in Malaysia are affected by the disease [6]. Host plant resistance offers the most viable, low cost effective and sustainable strategy to manage the disease than chemical control and biological method.…”

“…Widespread use of resistant cultivars leads to development of selection pressure in the pathogen that resulted into breaking of resistance barrier. Majority of R-genes are dominant in nature, but recessive gene has also been reported [6]. Dominant R-genes for BLB are xa-1, xa -3, xa-4, xa-7, xa-10, xa-14, xa-21 and xa-22(t) and some major recessive genes are xa-5, xa-13.…”

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

“…Rice serves as staple food crop and source of energygiving food for more than half of the world's population, which is over 3.5 billion people. The demand for rice is still increasing in Asia as the consumption rate is at least 90% and it is globally projected that the demand for rice will rise up to 650 million tonnes by 2050 [1]. At present, the population of the world is increasing geometrically and the demand for staple food like rice is also increasing, so bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv.…”

“…A genetic marker is any assayable phenotype or visible trait, for which alleles at individual loci segregate following the laws of Mendel. Marker assisted selection is a technique that helps to make conventional breeding more efficient but not a substitute for conventional breeding [1]. It offers genetic tools for selection of target genes from the existing germplasm that would be used in breeding activities but does not include genetic engineering which involves the transfer of isolated gene sequences [5,6].…”