Preparation Of Trichoderma Asperellum Microcapsules And Its Efficacy On Powdery Mildew

Trichoderma asperellum is a kind of widely used bio-control fungi.The usage of biological agents to control diseases and insect pests can avoid environmental pesticide pollution,pesticide residues and pesticide resistance.However,most biological agents are faced with problems such as short retention period and shelf life due to environmental and other adverse external factors.Therefore,T.asperellum microcapsules with high storage stability,good protective effect,long duration and environmental friendliness were prepared and conducted field efficacy experiments in this study.The main results were as follows.1.The sodium alginate was selected as wall material based on good biocompatibility to T.asperellum.The sodium alginate-T.asperellum microcapsules were prepared by sharp-hole method.The opimal preparation process of microcapsules was determined as follows:the concentration of sodium alginate was 1.0%,the ratio of core to wall was 2:1,the concentration of calcium chloride was 4.0%,and the curing time was 20 min.The T.asperellum microcapsules contain 2.53×10⁹/g of the loading capacity,18.33%of the water content and135.66%of the swelling rate.The 90.88%of the spores in the microcapsules could be released at the period of 15 days.The microcapsules were spherical and slightly depressed under SEM.The survival rates of heat storage for 15 days,UV treatment for 0.5 h,room temperature storage for 180 days and 4℃storage for 180 days were 22.92%,49.92%,36.26%and 42.13%,which were significantly 3.46%,26.64%,17.22%and 21.18%higher than that of uncoated fungi,respectively.2.The SA-chitosan/nano-chitosan-T.asperellum microcapsules were prepared in this study.The two microcapsules were spherical and the surface of the microcapsules embedded by nano-chitosan layer was smoother under SEM.The spore survival rate was 48.83%,78.61%,57.19%and 64.18%after 15 d of hot storage,0.5 h of UV treatment,180 d of room temperature storage and 180 d of 4℃storage,respectively.The spore survival rate of sodium alginate-chitosan-T.asperellum microcapsules was 46.73%,70.36%,50.48%and 56.61%after15 d of hot storage,0.5 h of UV treatment,180 d of room temperature storage and 180 d of 4℃storage,respectively.Nano-chitosan coating has better conidia protection and better controlled release than that of chitosan coating.Compared with single microcapsules,double-layer microcapsules have better protective effect on conidia,and the shelf life of sodium alginate-chitosan/nano-chitosan-T.asperellum microcapsules is significantly prolonged.3.The control effects of T.asperellum microcapsules on cucumber powdery mildew were evaluated by field efficacy test.Different doses of T.asperellum microcapsules have control effects on cucumber powdery mildew.The dose of 1.33×10⁹CFU/g T.asperellum microcapsules was 500 g/mu,and the control efficacy of microcapsules on cucumber powdery mildew was 75.63%,which could effectively control the occurrence and harm of cucumber powdery mildew.The control efficacy of the microcapsule on cucumber powdery mildew was similar to that of the wettable powder of 10¹¹CFU/g Bacillus velezensis with 50 g/mu.The preparation process of microcapsules obtained was simple,pollution-free with high storage stability and good microbial protection effect,which effectively extended the shelf life of the preparation,and provided a theoretical basis for the production and application of T.asperellum microcapsules.