| Bacterial leaf streak (BLS) is a quarantine rice disease caused by Xanthomonas oryzae pv. oryzicola (Xooc), which has characteristics of destruction, epidemic and outbreak in southern China. Available reports suggest that yield losses due to this disease typically range from15%to25%depending on the rice variety and climatic conditions. Under conditions favorable for spread, BLS may affect entire fields and cause damage reductions in grain weight of up to40%-60%. Variety resistance results from interaction between host and pathogen. The fundation of resistance gene distribution is to uderstand the varity of population genetic of plant pathogen. The main results were summarized as follows:Genetic diversity and pathotype variability of X. oryzae pv. oryzicola strains collected from Jiangsu, Yunnan, Jiangxi, Hunan and Anhui were analyzed by using rep-PCR fingerprinting techniques. Genomic DNA from sixty nine strains was amplified with two specific primers BOX and ERIC. Dendrograms were generated from the data by using UPGMA analysis. The strains tested were similar each other at a level of80%,10and8clusters were grouped with BOX and ERIC, respectively. The predominant groups were cluster3and5for each primer BOX and ERIC involving27(39.1%) and24(34.8%) strains, respectively. The genetic diversities of the population of tested strains were0.9784(for BOX) and0.9833(for ERIC), respectively. The results indicated that the genetic diversity of Xanthomonas oryzae pv. oryzicola was various. Sixty nine strains inoculated onto five differential cultivars including near-isogenic rice lines carrying single resistance gene, IRBB4, IRBB5, IRBB14, IRBB21and IRBB24, and a highly susceptible cultivar Jinggang30, may group thirteen pathotypes. The predominant pathotype was C6(26.1%). No relationships were observed between UPGM A groups (BOX and ERIC) of the69strains and pathotypes, but each group was partially associated with the regional origin of strains.To provide a theoretical basis for rice cultivar distribution and rapid identification of virulence of X. oryzae pv. oryzicola, The virulence differentiation of71isolates of Xanthomonas oryzae pv. oryzicola collected from Hunan, Jiangxi, Yunnan, Jiangsu and Anhui provinces were identified with six rice cultivars (Jingang30, IRBB4, IRBB5, IRBB14, IRBB21, IRBB24) containing different resistance genes against bacterial blight by the inoculation methods of leaf-infiltration with needleless syringes at seedling stage and leaf-needling at adult stage. The results showed that the71strains were classified into18pathotypes at seedling stage and13pathotypes at adult stage. The predominant pathotype was C1(17.0%of the total strains) at seedling stage, and C10(25.4%of the total strains) at adult stage. Most isolates had weak interactions with the rice cultivars, and some the isolates had specific interactions. However, for a single strain, the virulence differentiation of X. oryzae pv. oryzicola was not the same in different growth stages. It also found that all the strains were infected241times (the infection rate was56.6%) and245times (the infection rate was57.5%) at seedling and adult stages, respectively. The virulences of pathogenic bacteria in different rice varieties at seedling and adult stages were basically the same.In this paper,1173bacterial strains were isolated from the disease leaves infected by X. oryzae pv. oryzicola, the healthy leaves and the rhizosphere of rice plants sampled in Nanjing, Taizhou, Yangzhou and Suqian in Jiangsu province. Among the tested strains,12strains demonstrated high inhibitory activity agaimst X. oryzae pv. oryzicola. The Diameter of inhibition zones of4strains were more than27mm. Control efficiencies of strain Lx-11were62.5%and60.2%in pot and field trials, respectively, significantly higher than those of20%bismerthlazol treatment (51.2%and45.8%). Based on morphological, physiological and biochemical characteristics and16S rDNA sequence analysis, the strain Lx-11was identified to be Bacillus amyloliquefaciens.The Plackett-Burman experiment and response surface methodology were adopted to optimize the liquid fermentation conditions of the biocontrol agent of Bacillus amyloliquefaciens Lx-11. The results indicated that the temperature, the filling volume of shaking flask and inoculum volume were the major factors that affect the yield of Lx-11. The fermentation conditions were30.84℃, inoculum volume1.52%and the filling volume59.68mL in250mL shaking flask for48h, and initial pH at7.0. Under the optimized fermentation conditions the production of spores was up to3.75×109cfu·mL-1and the width of antibacterial activity was8.2mm. Fermentation experiments with shake flasks verified that there was no statistical difference between the yield value and antibacterial activity forecasted by the model. We found that Lx-11secreted three kinds of lipopeptides including surfactin, bacillomycin D and fengycin, which exhibted antibacterial activity against X. oryzae pv. oryzicola. The antibacterial activity could be associated with surfactin-lipopeptides, and practically abolished in surfacin-deficient mutants. In addition, the defense-related genes PR-1a, PR-1b, NPR1and PAL were concurrently expressed in the leaves of rice after treated with Lx-11. The results implied that Lx-11triggered a systemic immunization activity. |
