| Epicoccum nigrum, strain XF1 was collected as a potential biological control agent for the late blight of potatoes caused by Phytophthora infestans. This study focused on the inhibition and control effect of XF1 against P. infestans in vitro and in vivo, and preliminarily tested the solid-state fermentation conditions of XF1 as well.The interaction between XF1 and P. infestans mycelia were studied by means of the dual culture on slides. Results showed that the mycelia growth of P. infestans was inhibited by XF1 evidently, microscopic vision indicated the hyphae of P. infestans became stunted and distorted adjacent to the boundary of XF1 colony, and the protoplasm of P. infestans mycelia was degenerated in the inhibition zone. However, the hyphae of XF1 had no significant difference compared with normal ones. After 48 h incubation of conidia of XF1 on the membrane (molecular weight cut off 8000-14000) with RA (Rye agar) underneath, the extra cellular substances secreted by XF1 and penetrated into the RA through the membrane can significantly inhibit the direct germination of sporangia and cystspores of P. infestans, with inhibitory rate of 90% and 100%, respectively. Releasing of zoospores from sporangia of P. infestans was inhibited intensively by the conidia free filtrates of solid fermentation products of XF1 with wheat grains, the release rate was only 0.36%, so did on cystospore germination and germ tube elongation, with inhibitory ratio was 50% and 75%, respectively. Those results showed that the substances that intensely inhibited P. infestans can be produced by XF1 during growth, the action mode for inhibition, in other words, mainly relyed on antagonism.Results of detached leaves test showed that conidia suspension of XF1 with concentration of 1.0×107 conidia/mL and 1.0×108 conidia/mL could provide the same control effect on potato late blight with 0.2% Kocide DF under indoor conditions. The surface of selected leaves of potato cultivar in greenhouse were sprayed with conidia suspension of XF1 at different time and then detached and brought into lab inoculated with P. infestans. And it was showed that control effect decreased one by one of 1, 12, 24, 48 and 96 hours sprayed before inoculation. The conidia of XF1 did not germinate before inoculation, with germination ratio were less than 1%. However, after inoculation and incubated under wetness for 4 hours, germination of conidia of XF1 were promoted, the highest germination rate, showed by the treatment of 1 hour spray before inoculation, was 45.27%, which significantly higher than the treatments of 48 and 96 hours spray before inoculation (with germination rate were 23.56% and 19.26, respectively). In addition, conidia of XF1 loosed control effect against potato late blight after sterilize (121℃, 20 min). Therefore, it was indicated that only viable conidia of XF1 can have control effect against potato late blight, and the survival status (germination ability) play the critical role on its control effect against potato late blight. Lab test showed that the germination rate of conidia of XF1 would significantly decrease after irradiated by ultraviolet light (UV) for 24 h, which suggests that after spraying of conidia of XF1 on potato plants, UV may be one of the important factors on their viability and control effect on potato late blight.Production of conidia of XF1 was tested in solid-state fermentation with rye and wheat grains. It was showed that the highest conidia production obtained after 40 days fermentation with rye. While the conidia of XF1 have high viability from both of the two grains, germination ratio were higher than 90%.Based on this study, the prospects and problems of applying the XF1 into biocontrol of potato late blight on field were discussed.
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