Studies On The Hypovirulence Of Isolate Ep-1PN Of Sclerotinia Sclerotiorum And Its Potential For Biological Control

In this paper, hypovirulence of isolate Ep - 1PN of Sclerotinia sclerotiorum was studied through analysing the inheritance of hypovirulence, and the potential use of isolate Ep- 1PN to control Sclerotinia diseases also was evaluated. Results showed that:Sixty-nine protoplast regenerants of hypovirulent isolate Ep-1PN were studied in detail. Among them, 35 regenerants were totally recovered, and did not differ from normal isolate of S. sclerotiorum ; Only 16 regenerants were similar to isolate Ep-1PN; The others were thought to be partially recovered. The results suggested that the hypovirulence - associated genetic elements existed in the cells of isolate Ep - 1PN unequally, and some cells were shortage of the hypovirulence- associated genetic elements.1572 sexual progenies of isolate Ep -1PN were obtained through single-ascospore-isolation from seven apothecia. Most of them (99.2%) were proved to be normal, only fourteen progenies showed abnormal characterise;cs, and six from the fourteen were similar to isolate Ep-1PN. The results suggested that the hypovirulence of isolate Ep-1PN could not be transmitted to its sexual progenies smoothly, and also suggested that the hypovirulence-associated genetic elements were cytoplasmic elements.Hypovirulence and its associated traits of isolate Ep-1PN could be transmitted to normal isolate of S. sclerotiorum (i. e. isolate Ep-1PNA183) through hyphal anastomosis, and the transmitted isolates were converted into hypovirulence. Therefore, the cytoplasmic elements were transmissible.Three species of double-stranded RNAs have been isolated from isolate Ep-1PN, but not from normal isolate Ep-1PNA183 and isolate Let-27. The sizes of them were 7.4kb, 6.4kb and 1.0kb respectively. Three species of dsRNA similar to those of isolate Ep-1PN could be detected in isolate Ep-1PNA183 after being transmitted. This result suggested that the dsRNAs in isolate Ep-1PN were transmissible, and tightly associated with hypovirulence, which means that dsRNAs and hypovirulence were co-transmissible.A 7. 4kb dsRNA segment could be isolated from a totally recovered culture P68. While two species of dsRNAs (7. 4kb and 6. 4kb) were checked in a partially recovered culture, P108, and two species of dsRNAs (7.4kb and 1.0kb) were checked in another partially recovered culture C₂9-These results suggested that the 7.4kb dsRNA in isolate Ep-1PN was not responsible for the hypovirulence directly, while 6. 4kb and 1.0kb species of dsRNAs would be involved with the hypovirulence directly. When the colonies of C₂9 and P108 intermingled, their colony morphologies were changed to that of isolate Ep-1PN and three species of dsRNAs like those of isolate Ep-1PN could be isolated. According to the result, it could be concluded that: To express the hypovirulence of isolate Ep-1PN, at least two elements would be necessary, one existing in C₂9, and the other in P108. This suggested that the 6.4kb and 1.0kb dsRNA segments would determine the hypovirulence of isolate Ep-1PN.Among ninety six cultures derived from single-sclerotiorum-isolation of isolate Ep-1PN, twenty of them were proved to be recovered to different degrees, and one culture (SSD₅) was totally recovered, which was not different from normal isolate of S. sclerotiorum . Surprisingly, cultures derived from a sclerotium of isolate Ep-1PN showed highly diversity in growth rate, colony morphology and virulence. Among fifteen cultures of SA series, one (SA5) was totally recovered, and lost all dsRNAs segments; seven were proved to be almost normal. However, three species of dsRNAs could be checked in some of them. According to the results, S. sclerotiorum (isolate Ep-1PN) could positively discard or inact the hypovirulence - associated dsRNAs during the sclerotium - forming -stage and dormant stage.Two mutants which could resist the influence of hypovirulence - associated dsRNAs have been isolated from single - sclerotium - isolation (SSB9) and from a PDA slant in which culture SA12 (no difference from isolate Ep-1PN) was cultured a...