| Watermelon wilt (Fusarium oxysporum f. sp. niveum) is a devastating vascular soil-borne disease, and difficult to control. As Fusarium oxysporum is a soil inhabitant fungi, which has a strong ability to resist adverse environment, now, biological control is much more popular among people. As an important biological pesticide resource, actinomycete has obtained much more attention, especially when its preparation was available in the reality. Compared to the traditional pesticide, biological pesticide has more advantages, especially in the environmental compatibility and safety. However, it also has many problem and difficult to the production. Considering the complex and changeable situation in soil, single soil bacteria are not ideal, to enlarge the space of biological control agent with actinomycetes, improve the control effect and stability to watermelon blight, we study complementary combinations of many bacteria. This study starts from complementary combinations of different characters of many actinomycetes, combinat bio-control strains of bacteria with different characters, then use combination. Results provide theory basis for bio-control feasibility of compound bacterium agent for actinomycete preventing.1. Using the methods of antibacterial activity and colonization ability, we started our research on antagonistic activity, breeding conditions,and the growth rate, finally we selected three strains which had good characters: strain 15-3, with fast growth and reproduction, strong resistance,especially low nutritional needs; SC1-1 had relatively the strongest inhibition and drug resistance to watermelon Fusarium, and could creates Chitinas; SF6 was an endophyte actinomycete, and its promoting effect is significant.2. Through optimization of fermentation conditions platter, we identified best solid culture conditions of three actinomycetes:85% rice powder +12% rice bran and 3% shrimp meal; seed liquid:most suitable inoculum were 25%; the age of SC11 best seed liqid was 144h, strains SF6 and 153 were 96h; different strains have different optimal incubation time, as strains SC11 and 153 were 9d, SF6 was 8d. In the optimization of culture conditions, not only we had increased the number of actinomycete, accelerated growth and reproduction rate of strain, but also improved the biocontrol agents on target for inhibition of bacteria. 3. By plate culture, heat treatment, ultraviolet treatment method, we had screened out agents of the appropriate carrier. Among them, chitosan, non-farm soil and crude chitinase had the significant protective effect on the growth of actinomycetes. The powder was mixed with the carrier, 55±2℃heat storage for 7d, the three biocontrol agents have received a higher survival rate, with significant differences compared to the level of control, so we chose these three materials as common carrier of three biocontrol agents.4. As a consequence, we combine the three actinomycetes, by researching the fermentation, storage method and its antagonistic ability, we had studied the control effect of combining bio-control strains against Fusarium wilt of Watermelon and the promoting effect of watermelon. Pot experiment results showed that the composite agents and the three single strains on watermelon wilt disease control had certain growth-promoting effects, and the best dued to SC11 +153 + SF6 combined. Control efficiency of Composite agents is up to 47.47%, which is significantly higher than the control effect of a single strain of the best SC11 (25.87%). It suggested that strains could play a more desirable biocontrol effect through complementary synergies.
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