The Study Of Bacillus Antagonize Crown Rots Of Banana

The author collected banana samples from Dongfang, Ledong, Sanya, Qionghai and Chengmai, isolated pathogens from bananas which showed the symptoms of crown rot, cultured, measured and investigated the percentage and varieties of fungi. The results showed that the percentage was between 13.3 and 87.2, which in Sanya was largest; there were 6 species of Fusarium spp. in isolated 225 strains. After testing of pathogenicity and identification we take a conclusion that F. moniliforme var. subglutinans, F. semitectum, F.aquaeductuum and F.camptoceras were main pathogens of banana crown rot hi Hainan province.278 isolations were obtained from the soil close to the banana roots and the weeds in the banana plantation. Eight strains were found to have a strong antagonism to the pathogen of banana brown rot after fungus-bacterium pairing culture. Thought testing the antagonism to the pathogens of banana brown rot of the aseptic filtrate, there were 4 strains selected as biocontrol bacteria. They were identified as Bacillus stucilis based on their morphological features, cultural characteristics and physiological-biochemical properties.The F.spp. cultured on the PDA plate which contain the culture filtrate of B. subtilis stains B63,B68,B74,B75. After treated by the aseptic filtrate, there were a lot of vesicle like prayer beads appearing in the apex and middle of the mycelia of F. spp. and the diameter of the vesicle was four to five times of the normal hyphae'. As the time gone, the cell wall of the vesicles broken and the protoplasm in it flowed out. The spore suspension of F. spp. treated by asepticfiltrate of the biocontrol bacteria were cultured at 27 C then observed at regular intervals under the microscope. It was showed that some spore tubes began to dilate and become to deformed spherical structure when cultured for 12 hours and the spherical structures began to break after cultured for 18 hours ,the protoplasm of the cell flowed out and the cells were left as empty vesicles.Treated under 121 ,20 minutes and tested the activities of the aseptic filtrates, the results showed that the aseptic filtrates of B68 and B75 strains can not stand high temperature and their antagonism were lost after treated, the aseptic filtrates of B63 and B74 strains can bear high temperature of 121 C partly and their antagonism to F4 and F6 were lost ,but the antagonism-to F1 had no change between pretreatment and post treatment. This result can be explained as that the substances active to Fl of B63 and B 74 strains' aseptic filtrates had the bearing-high-temperature property, or explained as that the aseptic filtrates of B63 and B74 strains contained two ingredients of which one can bear high temperature but the other can not.The four Bacillus subtilis strains' antagonism to banana crown rot all exceeded 70 percent, which overran significantly that of Sporgon(52.63),the common used fungicide in commercial. The aseptic filtrates' antagonism were between 66.67 percent and 95.74 percent. The prevention of the aseptic filtrates which were not diluted by water were hightest, after diluted five times, their antagonism had no chang, but diluted ten times their prevention would descend remarkably.