Screening Of Bacterial Antagonists Against Fusarium Wilt Of Watermelon And The Research Of Its Bioactive Substances

Watermelon wilt disease is a soil epidemic which affects the growth of watermelon badly.The experiment was aim to obtain some high antagonistic strains and study their antibiotic substances.Firstly,strains library was established from healthy watermelon rhizosphere's soil .Secondly,some high antagonistic strains was obtained against fusarium oxysporum f.sp.melons from library by"bacterium to bacterium"biological control and the most antifunction strain-FM4 was picked out.At last,we did some research for FM4 in some aspects,e.g. resistance,identification,active substance isolation and purification,screening shake flask fermentation medium and fermentation conditions,utilization N⁺ injection to obtain high-product strain.Main conclusions are as follows:1.Our laboratory had obtained the 784 different types of bacteria by collecting soils from healthy watermelon rhizosphere, and then combining gradient dilution method and scribing isolation method in AnQing,HeFei,MaAnShan.Confrontation each other experiment show that there are 29 strains among them with antifunction .2.The morphous,cultivation characteristic,biology character and physiological and biochemistry nature of the FM4 were systematically evaluated according to"Bergey's ermination Bacteriology"and"Identification of Common Bacterial Systems Manual",The FM4 was preliminary identified as Micrococcus.3.By experiment research, we obtained a antifunction protein ,about 120kd,through ethanol precipitation and Sephadex G-150 .by mass spectrum initial identification, it show that this protein have a high semblance with Middle cell wall protein precursor (MWP),from Brevibacillus brevis.the antibiotic substance have higher stabilization at antibacterium,far-range temperature and pH. At 25-100℃, with the treatment temperature increasing, antimicrobial activity was stable trend, almost no change. PH of the tests showed almost antibacterial activity at a wide pH range, from pH2-10. Active substances has inhibitory effect on Escherichia coli, Staphylococcus aureus, Pichia yeast, Leuconostoc bacteria, Richter Trichoderma.4. This research used one-factor plus orthogonal design and RSM design exepirment,and finally identified the most suitab1e 1aboratory culture medium . the laboratory culture medium was: glucose 1.00%, peptone 2.23%, dipotassium hydrogen phosphate 0.01%, epsom salt 0.05 %. The most fementation condition was : initial pH7.50,170r/min,28.45℃,21.16h.5. According to the survival rate, 40×2.6×10¹³ ions/cm² N⁺ with 10 KeV energy was chosen as a suitable mutation factor. This thesis enriched the protecting methods in the ion beam implantation mutation.After first round N⁺ injection, we isolated 9 mutant strains,named:75,76,81,82,83,89,90,188 and 190.Through shake flask re-screening and generational stability experiment.Finally,we get one mutant strain-190,its vitality was correspondent to initial strain after going down to the future generation by twelve times.