| Epicoccum purpurascens is an important bio-control fungus. the protective effect of Strain XF1 of Epicoccum purpurascens, witch was collected in our laboratory, to the late blight of potatoes is well. To make for the E. purpurascens by further developing and utilizing, This study preliminarily tested different media in order to obtain optimal medium, which can product large amount of conidia of strain XF1 with high viability, and studied the storage conditions of conidia of XF1, providing material for the follow-up bio-control trials. Control efficacy of the conidia suspension of strain XF1 against potato late blight in the field was confirmed and the relationship between control efficacy and viability of XF1 conidia. Further studied the protective effect of UV protection for XF1 conidial in order to reduce the impact of UV on conidia of strain XF1, and improve the control efficiency of conidia in the field. The influence of the chemical agent against potato late blight was tested The research results are as following:In the five different media, yellow soya-bean medium was the most favorable one for mycelial growth, conidia production and conidia viability of strain XF1.The conidia of Strain XF1 by filtration and drying was stored at 4℃in darkness for one year, and their germination rates could still reach 86.57%, which meant this storage condition was good for conidia viability.The surface of selected leaves of potato cultivar in the field 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 control efficiency of the treatment of 1 hour spray before inoculation, the highest control efficiency , was 77.78% ; the control efficiency of the treatment of 12 hour spray before inoculation was 62.04% ; however, the control efficiency of the treatment of 36, 48, 96 hour spray before inoculation was in less than 25%. Under field conditions,the viability of XF1 conidia and control efficacy are consistent, the viability of XF1 conidial began to rapidly decline after 12 hour by spraying.The protective effect of ultraviolet protectant (UVP) combinations of 6 UV-absorbers and 4 light stabilizers against UV for conidia of E. purpurascens strain XF1 was tested in laboratory. The results showed that the protective efficiency of different UVP combinations was different,UVP combinations of benzotriazole and hexamethyl phosphorus triamide (a3b1) , and UVP combinations of oxybenzone and hexamethyl phosphorus triamide ( a4b1 and a5b1 ) , were confirmed to be more effective UV-protectants, with protective efficiency over 90% after 40-min exposure of UV light (atλ253.7 nm), and the protective efficiency of combined UVP of salicylic acid benzyl ester and hexamethyl phosphorus triamide (a1b1) was about 37.12% after 40-min exposure of UV light(atλ253.7 nm). UVP combinations without protective efficiency include combinations of salicylic acid benzyl esters and light stabilizer 770, benzotriazole and light stabilizer 770, benzophenones and light stabilizer 770 (a1b2, a3b2, a4b2, a5b2). The appropriate solvent combination was solvent n-hexane and peanut oil (1:1 , v/v) for selection of three complex UVP (a3b1, a4b1, a5b1), The effective concentration of a4b1 and a5b1 should be higher than 0.75% , while a3b1 should be higher than 1%. After 90-min and 180-min exposure of conidia to UV light(atλ253.7 nm), the protective efficiency of three selective UVP combinations could be over 88% and 63% - 66%, respectively.If the bio-control agent is used in the filed, you should not spray chemical pesticides such as mancozeb, dimethomorph and azoxystrobin, but cymoxanil and metalaxyl can. Because the inhibitory effect of cymoxanil and metalaxyl to the bio-control agents is weak. |
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