Preliminary Study On The Hypovirulent Phenotype Of Sclerotinia Sclerotiorum Strain Ep-1PN Influenced By Coniothyrium Minitans Strain ZS-1

Sclerotinia sclerotiorum(Lib.) de Bary,with a host range that including more than 400 plant species,is a destructive pathogen of many economically important crops.It is necessary 1o search for alternative,sustainable control measures for this soil-borne plant disease since chemicals are carrying more and more environmental problems. Coniothyrium minitans is a well-known mycoparasite of S.sclerotiorum,infecting sclerotia in the soil and reducing the viability of the pathogen.And it is an ecologically obligate mycoparasite and requires the similar living environment to its host.C.minitans has the ability and potential to control disease caused by S.sclerotiorum.Mycoviruses could reduce fungal virulence,and hypovirus-infected fungi could be used to control plant disease.Hypovirulent strain Ep-1PN of S.sclerotiorum contains three dsRNA fragments, namely SsRV-L,SsDRV and SsRV-S.It also has potential to control sclerotial disease.To evaluate whether the mycoparasitsm of C.minitans was compatible with the hypovirulent strain Ep-1PN,the influence of C.minitans ZS-1 to Ep-1PN was studied in this research.After the mycelium of Ep-1PN was parasited by ZS-1,approximately 16.1% colony could grow out strong and normal mycelium of S.sclerotiorum,while the ratio got up to 43.4%when sclerotia of Ep-1PN was treated by conidial of ZS-1.The strong and normal colony of S.sclerotiorum was isolated and biological characteristics were studied.Results showed the growth rate and pathogenicity of 34 such isolates were significantly different to that of Ep-1PN,and much more similar to the virus-free strain Ep-1PNA367.dsRNA fragment was analyzes by Northern blot with two probes,SsRV-L and SsDRV.These isolates could be divided into three types,3 out of 34 containing SsRV-L and SsDRV belonged to typeâ… ;17 out of 34 containing SsRV-L belonged to typeâ…¡;and the rest 14 containing no dsRNA fragment belonged to typeâ…¢. The Colony morphology,growth rate,and Pathogenicity of all the PRI recovered to normal leval,these isolates partly,or even totally discard the dsRNA segments. Forthemore,another hypovirulent strain SZ-150 of S.sclerotiorum was used to carry out the same test above.About 25.3%colony could grow out strong and normal mycelium of S.sclerotiorum after parasited by ZS-1.The results suggested that it may be a common phenomenon that the phenotype of S. sclerotiorum hypovirulent strain could recover after parasited by C.minitans.