Genetic Diversity Analysi Of Xanthomonas Axonopodis Pv.Manihotis Of Cassava

Cassava, yams (Dioscorea spp.) and sweet potatoes are important sources of food in the tropics.Cassava bacterial blight caused by Xanthomonas axonopodis pv. Manihotis (short for Xam)which generally occurs in the cassava growing areas in Asia and America, Africa is one of the most important diseases distributed at cassava-growing areas worldwide. cassava bacterial blight can cause up to12-90%crop loss.However, molecular pathogenesis of the pathogen is little known, which deterred the research and development of the prevention and control technology. Presently screening and planting resistant varieties is the most economic and effective approach to resist bacterial blight in cassava production. In order to understand the bacterial virulence differentiation and population structure of the different regions, as well as perform rational distribution of resistant varieties, rotation and mutual exchanges, it makes great sense to undertake the studies of genetic diversity, from which important forward-looking information derived would be necessary references for in-depth breeding strategy and continuous improvement of varietal resistance.In all,45strains of Xam used in this study were isolated from standard samples collected in the various parts of the world. We mensurated the reproduction rate, lawn color, viscosity and extracellular enzyme activity of45Xam strains. It is demonstrated that there is considerable variability in the growth rate of the45strains, even if among isolates from the same province. Most of the strains growth rate reached peak value after48h cultivation. XOO, XamGX11, XamGX29, XamGX36these4strains grow faster than other strains and their OD600peaked after24h cultivation. However,11other strains including XamJX01, XamHN03, XamHN05, XamHN08, XamHN09, XamGD05, XamGD11, XamGD13, XamGX03, Xam1232, Xam1235shared obviously lower growth rates than other strains, and the OD600could not peak even when they were cultivated for72h. Meanwhile, the lawn color and viscosity of the45strains could be classified in5forms, most of the strains fall into the form B, whereas form E occupies the least number of strains. There is no obvious mutualities lies between the lawn color&viscosity of the strains and the virulence&the growth rate. The plate detection experimental results of extracellular enzyme activity showed that the tested strains could produce extracellular cellulase, amylase and protease, secretion of extracellular polysaccharide could also be detected.We also analysised the genetic diversity of Xam strains by means of RAPD and Rep-PCR.2special primers ERIC, J3and8RAPD random primers were selected for PCR amplification of45Xam strains1genomic DNA. ERIC, IS and RAPD3kinds of molecular marker methods present30,29,236types of pattern separately. Fringed by bands similar rate of80%between each other, using UPGMA9clusters were revealed among45strains. Genetic clustering has certain relevance with geographic region strains with close geographic origins are often close to each other in genetic distance.According to the results of UPGMA clustering analysis, selects15cluster representative of the strains, preparating of bacterial suspension, choosing the healthy, fully expanded mature leaves of cassava with leaf cutting inoculation. Investigated the incidence after14d, according to the standard of grading. Clustering analysis pointed of view, the genetic distance with XOO closer, its pathogenicity intensified.