Screening And Biological Characteristics Of Antagonistic Strains For Watermelin Fusarium Wilt And Its Fermentation Conditions And Antibiotic Substance

Watermelon wilt disease is one of the most important factors of the continuous cropping obstacle of watermelon, which is seriously restricting the development of watermelon production. Therefore, the study of Watermelon wilt disease is of great significance to watermelon production.Two bacteria strains N8and H11capable of resisting watermelin fusarium wilt were isolated from healthy watermelin rhizosphere, with plate isolation, confront culture and inhibition zone method. On the basis of morphologycal, physiological and bioehemical characteristics as well as16Sr RNA sequence, strain N8and H11were identified as Bacillus subtilis.Biological characteristics of strains N8and H11were investigated respectively. Strains N8and H11could grow well under the condition of pH6.0-8.0. The optimum pH of N8was6.0, and21h could get to the stable period.The optimum pH of H11was6.0and18h could get to the stable period. The optimum temperature, inoculation amount and medium volume in bottle of N8and H11were35℃,5%and75mL/250mL respectively. Strains N8and H11could both tolerant ampicillin and many chemical pesticides.The antibiotic activity of strains N8and H11have higher stabilization at far-range temperature and pH.At30-121℃,with the treatment temperature increasing, antimicrobial activity was stable trend,almost no change. The pH of the tests showed almost antibacterial activity at a wide pH range from pH3-9, and the optimum pH of N8and H11were5.5and5-5.5respectively.Strains N8and H11are effective to six plant pathogens, which are Rhizoctonia solani Kuhn, Phytophthora capsici Leonian, Vermicularia copsici, Bipolaris maydis (Nishik.&Miyabe)shoem, Mycosphaerella melonis and Magnaporthe grisea (Hebert)Barr, by the inhibitory strip with a width of25mm.This research used one-factor plus orthogonal design and RSM design exepirment, and finally identified the most suitable laboratory culture medium and fementation conditions. The laboratory culture medium was:potato200g, sucrose20g, peptone5g, ammonium sulfate3g, potassium dihydrogen phosphate2g, water1000mL. The suitable fermentation condition was:30℃, the initial pH6.0,5%inoculation amount,75mL/250mL, and48h and72h as the suitable culture time of N8and H11respectively.The antibiotic substance was extracellular, it could dissolve in inorganic solvent such as water and organic solvent such as ethanol, etc. So the antibiotic substance could purified ulteriorly by using this deliquescent charcteristic.Fanally, the antibiotic substance could be obtained by silica gel TLC.By means of pot tests, control effect of strains N8, H11and the other strain of actinomycete on watermelon wilt disease was notable, the control rate were76.46%,57.65%å'Œ61.09%. Besides, if the antagonistic strains and organic fertilizer combined application, control effect will be significantly improved, and the control rate were increased10%.