| Melon wilt is a common soil-borne disease in melon production,with an incidence of50-70%,which seriously restricts the development of melon industry.Chemical control is often used in agricultural control,but chemical agents easily pollute the environment,reduce the quality of melon and make pathogens resistant to drugs when they are used for a long time.Therefore,there is a need for control methods in production that don’t pollute the environment and have no adverse effects on plants.Silver Nanoparticles（AgNPs）has been proved to be effective antimicrobial agents which can be synthesized by biosynthesis method.It can be combined with Trichoderma sp.to control melon wilt,so as to explore a new way suitable for controlling melon wilt.In this study,the fermentation broth of Trichoderma longibrachiatum was combined with silver nitrate to biosynthesis AgNPs.The synthesis conditions of AgNPs were optimized with orthogonal test,which were selected through three indexes:the synthesis amount of AgNPs,the antifungal activity of AgNPs against Fusarium oxysporum and comprehensive indexes.The AgNPs with better conditions were characterized and analyzed.At the same time,AgNPs was applied to melon plants to study the growth and development of melon and the control disease incidence of melon wilt.Then,the antifungal mechanism of AgNPs against F.oxysporum and the biosecurity evaluation of AgNPs by silkworm and tussah were studied.The results are as follows:1.The fermentation broth of T.longibrachiatum can effectively synthesize AgNPs.Data revealed that 2 mmol·L-1 of silver nitrate,55°C of the synthesis temperature,and p H 5of the synthesis solution were the optimum conditions for the synthesis of the silver nanoparticles.The synthesis of AgNPs reached 54.13 mg and the fungal inhibition rate reached 56.11%.The characterization analysis of AgNPs showed that the particle size of AgNPs was in the range of 25-35 nm,with good dispersion,spherical or pseudo-spherical shape,face centered three-dimensional structure,rich surface functional group structure and high stability.2.AgNPs synthesized by T.longibrachiatum had an effect on the growth and development of melon seeds.AgNPs of 25 mg·L-1could promote the germination and growth of melon seeds.The germination rate,root length and fibrous root number of melon seeds increased significantly.AgNPs could reduce the disease incidence of melon wilt.3.The antifungal mechanism of AgNPs showed that AgNPs could adhere to the cell membrane through the cell wall of F.oxysporum.Then,AgNPs destroyed the structure of cell membrane,resulting in the leakage of cell contents and the loss of soluble protein and soluble sugar in cells.AgNPs changed the SOD and POD enzyme activities of F.oxysporum,both increased first and then decreased,and the CAT enzyme activity showed a downward trend.4.The biosafety evaluation of AgNPs showed that low concentration AgNPs(100mg·L-1)had no effect on the growth and development of silkworm and tussah larvae,and there was no significant difference between silkworm larvae and the control group in weight,food intake,growth and development time and cocoon quality.The low concentration of AgNPs(100 mg·L-1)didn’t show significant difference in CAT enzyme activity of tussah larvae compared with the control,and POD and intestinal fluid protease activities were higher than those of the control.Comprehensive analysis showed that the biosynthetic AgNPs had no toxicity to silkworm. |
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