Screening And Fermentation Of Antagonistic Bacterium Against Muskmelon Bacterial Spot Disease In Xinjiang

Muskmelon is one of the famous speciality in Xinjiang. However bacterial spot disease, one of the serious bacterial diseases, restricts the development of Xinjiang muskmelon. F159 (Acidovorax avenae subsp. Citrulli), the pathogene of bacterial spot disease on muskmelon was isolated from muskmelon diseased leaves and identified through morphological observation, physiological and biochemical test, and 16S rDNA sequence analysis. Among 195 strains isolated from soil samples surveyed using agar plate method ,63 strains showed antagonism on spot disease, which inhibited the activity of pathogens causing bacterial spot disease such as bacterial fruit blotch pathogens(Acidovorax avenae subsp. citrulli)F159,B4 and angular leaf spot pathogen(Pseudomonas syringae pv. lachrymans)P4. Of these, 56 strains were confirmed to be bacteria, and 7 strains were actinomyces. The antagonistic bacteria G-14 and actinomyces P-13 exhibiting significant inhibitory to bacterial spot diseases on muskmelon were screened by reselection experiment with cup-plate method. Greenhouse experiments showed that effect of prevention of the antagonistic bacteria G-14 was better than that of the efficacy. According to the morphology, cultural characteristics, identification by using VITEK 32 and the 16S rDNA gene sequence analysis, the antagonistic bacteria G-14 and actinomyces P-13 belong to Paenibacillus polymyxa and Streptomyces, respectively.The growth conditions tests showed that the G-14 was facultative anaerobes, which the optimal incubation time was 20 h, the optimum temperature was 25°C to 28°C, the optimal pH was 6 to 7.The orthogonal experiment on fermentation conditions of antagonistic bacteria G-14 showed that the best fermentation formula of G-14 was as follows: cornflour 0.5% ,corn plasm 0.6%, sodium chloride 0.6%,MgSO4 0.175%, and K2HPO4 0.175%.