| Potato (Solanum tuberosum L.)is one of the four major food crops of the world, China is the world’s largest production base of potato.The United Nations named 2008 as "International Year of the Potato."The development of potato production was menaced by serious threat of some fungal diseases, in particular, the Phytophthora infestans, which resulted in a serious damage even extinction in production. Looking for biopesticide which could much more effectively prevent and control of archival vermins from metabolites of microbes was an important way to deal with this didease. Actinomycosis was the first micro-organisms for biological control,among them, Streptomyces had the most biocontrol valuable (Streptomyces spp.).The purpose of this study was to screen some actinomyces from the soil,which have a highly effective antagonist to P. infestans, and make it clera that control of the fermentation product on potato tuber slices and detached leaves against late blight, and then analyse the effect of environment conditions and reproduction times on activity of fermentation product, as well as some physical or chemical properties of fermentation product.It is helpful for separation and purification of the anti-fungal materials, and to provid a theoretical basis for developing an efficient and stable biopesticide which can effectively control P. infestans.In this study, the main results are as follows:1 A total of 97 strains of P. infestans from the 192 samples were isolated by useing the selective medium (SRA) adding some antibiotics, and the average isolating rate reached up to 51%.2 Eighty four isolates of actinomyces were separated and purificated from nine soil samples in five regions.36 of 84 isolates had the evident inhibition on P. infestans, the inhibition rate of which reached up to 65% by using dual-culture method and anti-fungal activity of fermentation. An isolate of them, NB8 strain had the strongest inhibition on P.infestans, and the inhibition rates of its vital and fermentation were 97.33% and 92%, respectively.3 Preventive and therapeutic effect of NB8’s fermentation on potato tubers and detached leaves were investigated in this experiment. On tuber slices, the preventive effect was 22.19% and on the detached leaves that was 63.43%.The therapeutic effect was not very strong. But the preventive effect and therapeutic effect of NB8 fermentation was much better than that of Alternaria kikuchiana A204 and A.brassicicola A206 which were selected in previous experiment.4 NB8 strain was classified as the Streptomyces albus,based on morphological,cultural, physiological,and biochemical characteristics.5 Optimum cultural time of NB8 was determined as follows.The seeds liquid was to culture for 5 d,and to expand culturing for 10 d.And the inhibitory rate could reach up to 93% at the optimum condition.6 The effect of environment and reprodution on inhibition activity of NB8 fermentation was investigated with filter method.The inhibition activity of NB8 fermented product on P.infestans was stable and resistant to ultraviolet radiation, high-temperature, and low pH.Its inhibition rates could reach up to 81.20% and 78.67%, in treatment of ultraviolet radiation (30W,30cm for 10h) and temperature (100℃for 60 min), respectively. In addition, antifungal activity of NB8 fermentation did not change at room condition in storing for 2 months, or reproduction for 10 times.7 The fermentation product of NB8 was pre-treated with 90% of ethanol and then its characteristic was analysed with following methods. The active component in fermentation was dertermined as a kind of non alkalic antibiotics according to Dosko solvent system.The Rf value of active ingredient in fermentation was the largest in the water by Betina chromatography solvent system, and it was supposed that the component could be the water-soluble group of antibiotics.While the Rf value of pH paper chromatography increased with pH decreasing, and it is similar to acid group of antibiotics. |
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