Preliminary Study On Interspecies Transmission Of Sclerotinia Sclerotiorum Debilitation-Associated RNA Virus (SsDRV) From S. Sclerotiorum To S. Nivalis

Sclerotinia sclerotiorum hypovirulent strain Ep-1PN carries two mycoviruses,one of which,SsDRV,is associated with virulence debilitation,and the other mycovirus SSRV-L is not.As mycoviruses are not transmitted by any extracellular route,they were transmitted through hyphal fusion or anastomosis horizontally,or through asexual reproduction vertically.However,the complexity of vegetative incompatibility limits the spread of mycovirus among different strains of fungus.In preliminary studies,our lab found that when Ep-1PN strain was pared with Sclerotinia nivalis strain Let-19, subcultures from the colony margin of strain Let-19 appeared debilitated phenotype. Strain Let-19 and strain Ep-1PN belong to the same genus but different species.As mycoviruses in strain Ep-1PN may be transmitted among the two species,in this paper, we studied the interspecies transmission of mycoviruses,and the results were as follows:1.When S.nivalis strain Let-19 was dual cultured with S.sclerotiorum hypovirulent strain Ep-1PN,its subculture Let-19V showed a phenotype different from normal virulent strain Let-19.Let-19V was found to grow slower than original strain Let-19, and developed an abnormal colony significantly different from its origin,with the virulence of Let-19V also debilitated.The debilitation showed by Let-19V could be transmitted to Let-19 strains through dual culture.2.The mycelia of Let-19V was harvested to extract dsRNA sample,and electrophoretic analysis showed that Let-19V carried two segments of dsRNA,one of them was about 6.4 kb,which was similar to that in hypovirulent strain Ep-1PN which was proved to the replication form of SsDRV.No similar dsRNA segment was found in original strain Let-19.Northern blot analysis confirmed that the 6.4-kb dsRNA segment in Let-19V was transmitted from that in hypovirulent strain Ep-1PN.Thus,the mycoviruses in S.sclerotiorum were transmitted to S.nivalis intrespecifically.3.The frequency of interspecifical transmission of mycovims were examined through dual culture on PDA plate and dual inoculation on leaves of lettuce.The results showed that the frequency on PDA plate and on leaves were 27%and 23%, respectively.As lettuce is host of S.sclerotiorum and S.nivalis,so we predict that natural interspecifical transmittion of rnycoviruser is very possible.Mycoviruses can transmit from strain Ep-1PN to a different species S.nivalis in such a high frequency indicates that the vegetative incompatibility is not an absolute obstacle for interspecific transmission of mycoviruses.Our finding will provide new clues and ideas to break the obstruction of vegetative incompatibility among different fungal strains. Our funding also showed that SsDRV could replication in fungi rather than S. sclerotiorum,which may provide a certain theoretical basis for the possibility of using mycoviruses to biocontrol Sclerotinia disease.