Biocontrol Action Of Two Trichoderma Species Against Fusarium Oxysporium F. Sp. Cucumerinum And The Effects On Soil Microorganisms In The Rhizosphere

Cucumber Fusarium wilt is one of the most common and serious soilborne fungal diseases of vegetables in greenhouse. Its effective control had become the difficult problem to be solved eagerly in vegetable production. The strain No.2 of Trichoderma longbrachiatum and strain No.4 of T. citrinoviride screened by Agricultural Culture Collection of China (ACCC) and have growth-promoting and disease resistance-inducing effects on a variety of vegetable. In this paper, the interaction between the two Trichoderma species and Fusarium oxysporium f. sp. cucumerinum was studied. The enzymes related to inducing disease resistance in cucumber plant were studied at different growth stages of cucumber. At the same time, the effects on soil microbe were studied after Trichoderma longbrachiatum was applied through detecting the rhizosphere soil enzymes activities and analysing rhizosphere soil microbial communities at different growth stages of cucumber. The results will clarify the biocontrol mechanisms of the two Trichoderma species and establish basis for effective utilization of Trichoderma longbrachiatum. The main research results are as follows:The results from dual culture, microscopic observation and inhibition tests showed that competition and mycoparasitism were the important mechanisms of the two Trichoderma species against pathogenic fungi, and antibiosis was also existed. The chitinase activity andβ-1, 3-glucanase activity of the two Trichoderma species were determined with the method of reducing sugar. The results indicated that the change tendency of the two enzymes activities of the same strain were roughly same at different fermentation time. At the same fermentation time, the chitinase activity of strain No.2 was lower than that of strain No.4, and theβ-1, 3-glucanase activity was reverse. Combining with the early research results, we could learn that there was no simple corresponding relation between the ability to biocontrol fungal diseases and the activities of chitinase andβ-1, 3-glucanase of the strains.The activities of enzymes related to inducing plant disease resistance were determined at different cucumber growth stages after Trichoderma longbrachiatum was applied. The results were that the phenylalanine ammonia-lyase (PAL) activity significantly increased, and the PAL activity of rootstock at seedling stage and that of leaf at flowering stage increased most distinctly. The enzyme activities of the treatment were 1.33 units and 1.11 units higher than those of CK respectively. The superoxide dismutase (SOD) activity of rootstock and leaf significantly increased, and the SOD activity of rootstock at final stage and that of leaf at fruiting stage increased most distinctly. The enzyme activities of the treatment were 10.32 units and 18.81 units higher than those of CK respectively. The activities of peroxidase decreased and the activities of catalase increased at seedling stage. The results showed that the disease resistance was induced and the ability of disease resistance was enhanced after Trichoderma longbrachiatum was applied.The activities of urease, catalase and acid phosphatase in rhizosphere soil were determined at different cucumber growth stages after Trichoderma longbrachiatum was applied. The results were that the urease activity of treatment was higher than that of CK at seedling stage and final stage. And the urease activity of treatment was lower than that of CK at flowering stage and fruiting stage. The catalase activity of treatment was higher than that of CK at all growth stages. The acid phosphatase activity of treatment was lower than that of CK at all growth stages. And the acid phosphatase activity changed significantly at flowering stage, the maximum decrease up to 20 enzyme activity units.The rhizosphere soil microbial communities were analysed by plate count, DGGE and Biolog methods. The results showed that the numbers of bacteria, actinomyces and fungi were all lower than that of CK in rhizosphere soil; In non-rhizosphere soil, the numbers of actinomycetes and fungi were lower than that of CK while the number of bacteria was higher than that of CK; the diversity of bacteria decreased slightly, while that of actinomycetes and fungi increased gradually in the cucumber rhizosphere soil; the ability to utilize carbon sources of soil microorganisms increased at seedling stage and decreased at the other stages after Trichoderma longbrachiatum was applied.