Study On Screening Of Biocontrol Actinomyces For Watermelon Fusarium Wilt And Their Prophylaxis And Growth Promoting Effect

Watermelon fusarium wilt is one of the most important factors of the continuous cropping obstacle of watermelon, which is seriously restricting the development of watermelon production. In order to obtain some high efficient actinomyces strains against watermelon fusarium wilt, some biocontrol actinomyces were screened. Then their prophylaxis and growth promoting effect on watermelon was studied.The result showed as following:1. In this paper, target pathogens were verified according to Koch's postulate. The results showed that both X1,X2,X3 were Fusarium oxysporum schlechlendahl f. sp. melons (Leach at currence) snyder et Hansen. Pathogenicity test showed that pathogenic intensity X1>X3>X2, the pathogenesis latent period of X1 was shortest, so it can be used as pathogens and target pathogens of biological activity assay for the further experiments.2. During the screening of more than 100 strains antagonistic actinomycetes by agar block method on culture dishes, 21 strains strongly antagonistic actinomycetes were obtained. The antibacterial circle diameter of Act1 and 28G336B respectively reached 24 mm,19 mm. The inhibition rate of fermentation broth against target pathogens of 14 actinomyces strains were determined by plate growth rate method. The results showed that all of fermentation broth had inhibition, the highest being 85.7 %.3. All of the inoculation with spore suspension of actinomyces had prophylaxis effect on watermelon seedling. Act1, Act11 and Act12 had no pathogenicity for watermelon. The infection of X1 could be inhibited by treatment of Act1 and delayed by treatment of Act11 and Act12.4. Both inoculation with spore suspension and live actinomyces preparation had promoting effect on watermelon.The plant height and dry weight significantly increased 32.8 % and 66.7 % in the treatment of inoculation with spore suspension of Act1,Act11 and Act12 compared with CK.The plant height and dry weight significantly increased 59.3 % and 59.8 % in the treatment of live actinomyces preparation compared with CK. 5. Inoculation with live actinomyces preparation had significant effect on the PPO activity and the soluble protein content of watermelon.The PPO activity of leaf and root respectively increased 2.0 %~81.8 % and 0.6 %~13.6 % in treatment of live actinomyces preparation.The PPO activity of leaf increased 8.7 %~30.6 % in treatment of foliage spray by fermentation broth of 5 actinomyces strains.The promotion of PPO activity was beneficial to improving disease resistance of watermelon. Inoculation with live actinomyces preparation lead to the desease of the soluble protein content of watermelon. The soluble protein content of leaf and root respectively decreased 9.2 %~52.5 % and 36.7 %~83.3 % in treatment of live actinomyces preparation.6. The dysbiosis of watermelon rooting zone leaded to soil borne disease.There were significant differences of microbe quantity and fungi flora between alternate cropping healthy and continuous cropping diseased watermelon rooting zone. The results showed that, the quantity of bacteria,fungi and actinomyces of rooting zone of watermelon continuous cropping for 2 years were rifely higher than those in the alternate cropping healthy CK. The quantity of bacteria,fungi,fungi of root surface,actinomyces increased 128.0 %,,55.1 %,126.0 %,90.8 % respectively. The fusarium number of rhizosphere soil and root surface soil of continuous cropping diseased watermelon plant was about 5 and 4 times higher than that of alternate cropping healthy watermelon plant. The fungi species of healthy watermelon rooting zone showed more multiplicity. The physiological combination of rooting zone micro-community keeps normal. Fusarium was a dominant species in fungi flora of diseased watermelon rooting zone, while other fungus quantity reduced quickly. The rooting zone micro-community of diseased watermelon had transformed into pathological combination, which increase the rate of soil borne disease of watermelon root.7. Inoculating with bio-control actinomyces on microbial flora of watermelon rooting zone had significant effect. The results showed that inoculating with Act1 in nursery bed soil had raised bacteria and actinomyces number of rooting zone soil of watermelon, reduced fungi number of rooting zone soil of watermelon. The quantity of bacteria increased by 48.7 %~651.6 %, thereinto the quantity of gemma bacillus of watermelon root surface soil was 8 times more than CK, the quantity of actinomyces increased by 17.8 %~478.4 %, the quantity of fungi decreased by 29.2 %~45.2 %, thereinto the destiny of Fusarium in the watermelon rhizosphere soil and root surface soil decreased markedly by 55 %and60 %, respectively. B/F increased by 75.4 %~369.5 %. 100 days after inoculation, the number of Act1 was more than 106·g-1. These results demonstrate an expectant colonization stability of Act1. After inoculation with Act1, the microbial flora of watermelon rooting zone soil changed markedly, it changed from fungi type to bacteria type. In watermelon rooting zone soil, a biological barrier formed mostly by bio-control actinomyces against soil borne plant diseases such as watermelon Fusarium wilt.