Research On Biological Control Of Sclerotinia Stem Rot Of Oilseed Rape With Sclerotinia Sclerotiorumdebilitation-Associated RNA Virus

The use of hypovirulence-associated mycoviruses from Sclerotinia sclerotiorum is an important way of biological control for sclerotinia stem rot (SSR). In this study, we have developed a method of biological control by using Sclerotinia sclerotiorum debilitation-associated RNA virus (SsDRV), and evaluated potential applications of mycoviruses as a biocontrol agent (BCA) to control SSR from the perspective of ecology. The main contents and results are given below.First of all, this present research confirmed that the conditions of environment and inoculation, such as incubation time of fungi, temperature, humidity and inoculation concentration of fungal hyphal fragments, effected fungal growth and pathogenicity. The results showed that the temperature at25℃, the relative humidity more than75%, the incubation time up to5days, and the inoculation concentration of hyphal fragments of1000mg/ml were the most suit conditions for fungal growth and pathogenicity. Under such conditions, SsDRV controlled SSR of oilseed rape successfully.Secondly, this research studied ecological characteristics of hypovirulent strain Ep-1PN of S. sclerotiorum under field conditions in detail. The results indicated that hyphal fragments of strain Ep-1PN could survive for more than5days on petals of oilseed rape, and maintain a high survival rate. Spraying hyphal fragments of strain Ep-1PN at the flowering stage of oilseed rape could suppress the infection of virulent isolates of S. sclerotiorum. In addition, the present results also confirmed that the application hyphal fragments of strain Ep-1PN with concentration of20mg/ml, the effect of biological control was the best under field conditions. However, the pathogenic capability was too execrable to cause diseases; and moreover, the germination dynamics test of sclerotia of strain Ep-1PN also revealed that the germination percentage was very low compared with that of virulent strain under field conditions. Therefore, biological control for SSR with strain Ep-IPN had low risk for oilrape seed.Finally, the present study evaluated efficacy of SsDRV as a BCA to control SSR in the field. The results showed that during the conditions of climatic factors that were suit for the occurrence and epidemic of SSR, strain Ep-1PN had control efficacy against the fungus of S. sclerotiorum at the flowering stage. The incidence and disease index of SSR treated with strain Ep-1PN at the flowering stage of oilseed rape was28.50%and20.80, respectively. The incidence and disease index of SSR treated with strain Ep-1PN was higher than that with the chemical control at the flowering stage. However, compared with application with Ep-1PN at budding stage and control treatment, the incidence and disease index was significantly lower.