Research Article Open Access Gao and Sun, J Rice Res 2013, 1:1 http://dx.doi.org/10.4172/jrr.1000104 Review Artcle Open Access Rice Research: Open Access Volume 1 • Issue 1 • 1000104 J Rice Res ISSN: JRR, an open access journal Keywords: Bacterial blight; Resistance; Somaclonal variation; Xa-25; Molecular mapping Introduction In 1884, bacterial blight (BB) in rice, caused by Xanthomonas oryzae pv. oryzae, was frst reported in Fukuoka, Japan. Up to date, bacterial blight is considered to be one of the most destructive diseases of rice worldwide, especially in South and Southeast Asia [1,2]. In some cases, this disease can cause 30 to 50% yield loss [3], and has been a serious threat to sustainable rice production. In addition to its economically importance, Xanthomonas oryzae pv. oryzae has been used as a model organism for host-pathogen interaction studies, in particular afer the full-length sequences of both rice genome [4,5] and bacterial blight genome [6,7] were available publicly. In China, bacterial blight was initially discovered in 1900 in the Guangdong province. Since then, bacterial blight has become a serious problem in all rice growing areas, especially in the central, east and south China [8]. Due to a wide utilization of susceptible cultivars, overuse of chemical fertilizers and other factories, bacterial blight was introduced and spread to new regions. Te use of resistant cultivars is the most economic and environmentally friendly strategy to control the disease. So far, at least 29 major resistance genes have been identifed in diferent rice varieties, and 6 of them have been cloned [9]. However, some bacterial blight resistance genes, such as Xa-1 and Xa-2, don’t confer resistance against BB strains that occur in China (see data below), and the resistant resources which can be used to control the disease are limited. Terefore, identifcation and application of new resistance genes has become an important and urgent task for rice breeders and geneticists in China [10]. Many plant cells have the ability and possibility to regenerate a whole plant under certain conditions. Tis phenomenon has been well known as plant totipotency. Based on the totipotency theory, cells of the organisms reproduce with almost exact fdelity and give rise to daughter cells of the same genotype. In general, plants derived from the same cultured cell exhibit identical or similar phenotypes. Based on this theory, in vitro culture technique has been developed and widely used to rapidly propagate plants with some valuable performances for commercial applications and scientifc researches. However, not all regenerated plants from a given genotype display the same phenotype in every operation. Some plants may exhibit diferent characters from the wild type, and in some cases, the diferences can be dramatic and obvious. In early studies, this kind of change was misunderstood as pollen contamination or residual mutations. Neverthness, when more and more such variations were observed in a variety of plants, including many self-pollinated plants such as rice, wheat, and barley [11-13], Larkin and Scowcrof [14] termed variation among plants regenerated from in vitro culture as somaclonal variation. It provides a powerful and complementary tool to create novel variations that would be hard or impossible to generate by conventional plant breeding. Now somaclonal variation has been widely used in rice breeding programs, including development of rice varieties for disease resistance. Somaclonal variation is unpredictable in nature and can be useful or useless for plant breeding programs, depending on the stability of the variation. In this respect, somaclonal variation is similar to that induced by chemical or physical mutagens [14-16]. Some mutants with variable characters such as fertility, fowering date, plant height or other morphology characters can be easily identifed in the feld. Tese variations are usually identifed based on phenotypic changes of regenerated plants, a strategy known as in vivo selection. However, other somaclonal mutants, such as physical or biochemical mutations (mutations in enzyme activity, seed acid amino content, etc), cannot be detected easily based on phenotypic changes. In addition, frequency of a specifc desirable variation is usually fairly low. Terefore, it is difcult and time-consuming to identify chemical or physiological mutants from many regenerated plants. In order to resolve this problem, in vitro selection strategy was established. Based on this strategy, calli were cultured on the media containing certain stress factors (antimetabolites, toxin, salt, etc) at an early developmental stage. As a result, only the callus resistant or *Corresponding author: Dongying Gao, Center for Applied Genetic Technologies, University of Georgia, USA, E-mail: dgao@uga.edu Received June 17, 2013; Accepted August 02, 2013; Published August 09, 2013 Citation: Gao D, Sun L (2013) In vitro Screening and Molecular Characterization of a Bacterial Blight Resistance Gene in Rice. J Rice Res 1: 104. doi: 10.4172/ jrr.1000104 Copyright: © 2013 Gao D, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract Bacterial blight (BB) is one of the most serious bacterial diseases of rice in the world. Since 1986, our laboratory has conducted in vitro screening and application of BB resistance somaclonal mutants for rice breeding. In this paper, we review our nearly 30-year research on BB resistance somaclonal variation, including the development of an in vitro selection system, discovery of BB resistance mutants, evaluation of BB resistance in a somaclonal mutant named HX-3, genetic analysis and molecular mapping of the new BB resistance gene Xa-25. In addition, we also used the new resistance gene to develop BB resistance cultivar and hybrid rice. Our long-term research contributed a novel resistance gene in rice, it also provided an example for new gene creation and discovery using somaclonal variation. In vitro Screening and Molecular Characterization of a Bacterial Blight Resistance Gene in Rice Dongying Gao* and Lihua Sun Jiangsu Academy of Agricultural Sciences, China