Synergetic Effect And Mechanism Of Dazomet And Clonostachys Rosea Against Cucumber Fusarium Wilt

The increasing soil-borne diseases in protected field have become serious problems that limited the production of vegetables in China. Soil fumigation and biological control are primary and effective ways to manage the disease。However, some weakness exists for both measures. In this study, a practice of combining fumigant Dazomet and bio-control agent Clonostachys rosea67-1against cucumber Fusarium wilt extensively occurring in greenhouse was evaluated, and synergetic effect and mechanism of the integrated management were demonstrated.The results showed that when Dazomet and biological fungus C. rosea67-1were applied at the concentration of1g.kg-1soil and106spores.g-1soil, respectively, the death rates of cucumber seedlings sowed in Foc KW2-1inoculated soil were13.3%and48.9%in30d, respectively, compared to0when the fumigant and bio-control fungus were used successively and73.3%in the control treatment inoculated with KW2-1only. The death rates among different treatments were significantly different (P<0.05), indicating that the combination of fumigation and biocontrol could effectively reduce the probability of infection of cucumber seeds and seedlings by Foc. In another pot trial, wealthy cucumber seedlings planted in seedbed for14d were transplanted into Foc infested soil, and disease index was determined in45d. The control efficiency of combination of Dazomet and67-1, Dazomet, and C. rosea67-1to cucumber Fusarium wilt reached100%,89.5%, and70.6%, respectively, with the number of pathogen in soil fell to11.9%,23.6%and1.2%.In an infected vegetable greenhouse the effectiveness of different practice was evaluated. In the treatment of Dazomet+C. rosea, the control efficacy reached98.5%, while in the treatments with fumigation or biocontrol agent, the efficacy were88.8%and62.2%, respectively. Analysis of Bliss Independence indicated that there was a synergetic effect of Dazomet and C. rosea conflicting cucumber Fusarium wilt. The cucumber yield increased by37.5%, which was significantly higher than fumigation treatment (P<0.05).The populations of biocontrol isolate and pathogen were determined as well. The number of C. rosea67-1in soil was5.9x104CFU.g-1soil in the combined application, significantly higher than single biocontrol treatment. The population of Foc decreased sharply after Dazomet fumigating, and the following introduction of C. rosea helped to suppress the pathogen to a low level. However, in the treatment without bio-agent, the numbers of Foc increased30-fold.Furthermore, chemical fumigation and biological control also affected soil micro-ecology. The monitoring of soil microbial flora demonstrated that after Dazomet plus67-1treatment, the population of bacteria in soil increased, while the number of fungi kept unchanged, implying that soil health indication enhenced.To illustrate the synergetic mechanism of weakening of the disease, the effects of chemical fumigation on colonization potential and activity of Foc was investigated. The results showed that after fumigating, the pathogenic fungus grew slowly with the increase of the concentration of Dazomet. An isolate KW2-1-F, dealt with100mg Dazomet per lkg soil, was acted as mutant strain to analyze the biological characters of fumigant-treated Foc.The microstructure of the pathogens with and without fumigant-treatment showed significant difference under SEM. The cells of KW2-1-F were seriously disturbed by Dazomet fumigation, most of which shrank, deformed, and even emptied, and organelle lysis and cell contents release were observed. Chemical fumigation made the level of sporulation of Foc declined sharply by94.4%. Meanwhile, both the pigment yields and the activity of3-D-glucosaccharase in KW2-1-F were significantly decreased by more than50%. After soaking in spore suspension of KW2-1and KW2-1-F, the germination of cucumber seed decreased in some extent. The seedlings treated by KW2-1were coated with white mycelia, and the plants were withered and dead in120h. While there was few mycelia associated with the plants with KW2-1-F treatment, and the growth of seedlings was healthy. Cucumber seedlings were infected by the pathogen of F. oxysporum. After transplanting for14d, more than70%seedlings treated with original strain showed up obvious wilt symptoms, and disease index reached74.0. On the other hand, only slight spots could be seen on the seedlings sinking in KW2-1-F suspension and its disease index only got to10.5, with an obviouse decline. The effect of fumigation on interaction between Foe KW2-1and biocontrol isolate67-1was also determined. The result demonstrated that the endurance of fumigated pathogen to C. rosea decreased compared with un-fumigated isolate.