Pathogenicity Of The Sclerotinia Sclerotiorum Isolates On Cabbage And Savoy And Their Sensitivity To Three Fungicides

Cabbage(Brassica oleracea L.var.capitata L.),native to the Mediterranean coast,is widely cultivated in China.Cabbage is the king of nutrition and contains a variety of protective compounds that are effective in preventing cancer and heart disease.At present,the annual planting area of cabbage in China is about 900,000 hm~2.Savoy(Brassica campestris L.ssp.chinensis var.rosularis Tsen),is one of the most important vegetables in winter.Sclerotinia sclerotinia is an important disease of cabbage and Savoy.Sclerotinia stem rot disease caused by Sclerotinia sclerotinia,which has become one of the main factors limiting vegetable production.Sclerotinia stem rot leads to the decrease of vegetable yield and even no yield.In the early stage of Sclerotinia stem rot,the symptoms was watery and light brown spots.When humidity was high,white floc hypha appeared in the sclerotiformis with black rat dung.In recent years,the occurrence of Sclerotinia stem rot on cabbage and broccoli has become more and more serious in Anhui Province with the growing area of cabbage and savoy.In this study,the isolates of Sclerotinia sclerotiorum were recovered from the disesed tissues of cabbage in main production areas of Anhui province.The pathogenicity of isolates of S.sclerotiorum were tested and determined on different cabbage varieties by pot inoculation.Furthermore,it was determined for the sensitivities of representative isolates to sclerotium,carbendazim and dimetriamine by mycelial growth rate method,.The main research results are as follows:1.Isolation and identification of Sclerotinia sclerotiorum isolates from cabbage and savoyThe diseased plants with typical symptoms were collected from cabbage and savoy fields in Huaiyuan,Panji,Shouxian and Hefei,Anhui Province.A total of 35 strains were isolated by tissue separation.Among them,the colony morphology of 35 strains was consistent,the colony was white and grew rapidly.The initial colony morphology is mycelium aggregated to form white protrusions and some of the protrusions had transparent liquid beads.Later the color of the protrusions became black and arranged in a ring around the colony.The ITS sequence of genomic DNA of the strain was blasted on NCBI,and the homology with the r DNA-ITS sequence of Sclerotinia sclerotiorum(HQ833448)was 99.26%.The isolates were further identified through pathogenicity test,morphological characteristics,sequence analysis of the internal transcribed spacer region of the ribosomal DNA(r DNA-ITS)and phylogenetic analysis based on r DNA-ITS sequences.The results showed that the pathogen causing Sclerotinia stem rot was Sclerotinia sclerotiorum.2.Pathogenicity assaysThe pathogenicity of 35 isolates of S.sclerotiorum were determined on 9 different cabbage varieties by pot inoculation.The virulence differentiation of the tested strains was significant and could be divided into three types:strong(disease index 70–100),medium(disease index 30–70)and weak(disease index 0–30).There were significant indigenous differences in the virulence of different strains to the same variety of cabbage.For example,the variety of‘Gangtou 50’,HY1-1,HY1-2 and other 10 strains showed strong virulence on this variety,while HY1-3,HY2-2 strains and 8 other strains showed weak virulence,and the other 6 strains showed moderate virulence.The virulence of the same strain to different cabbage varieties was also different,strain HY2-2 showed high virulence in 5varieties including’Gangtou 50’and’Jingfeng No.1’,weak virulence in 3 varieties including’Bochun’and’Chunfeng’,and moderate virulence in’Fangzhen’.3.Biological characteristics of Sclerotinia sclerotiorum isolatesIn this experiment,the temperature,p H,light and the utilization of carbon source of sclerotinia sclerotinia isolates were measured.The results showed that 25℃was the optimum temperature for mycelium growth of sclerotinia sclerotinia,and when the temperature was 35℃,mycelia stopped growing.Optimum p H for Sclerotinia sclerotinia at p H 6.When p H is>7,the higher the p H value,the slower the mycelia growth rate.Sclerotinia sclerotiorum grew fastest on the medium with fructose as carbon source,and the mycelium grew slowest on the medium with starch as carbon source.4.Sensitivity of Sclerotinia sclerotiorum isolates to three fungicidesIn this study,the sensitivity of 15 isolates to three fungicides was determined by mycelial growth rate method.All tested isolates were sensitive to the three fungicides,and highly sensitive to carbendazim,with EC50 value ranging from 0.0364 to 0.1080μg/m L.The EC50ranges of dimetriamine and boscalid were 0.0554～0.1377μg/m L and 0.0739～0.1891μg/m L,respectively.