Identification Of The Pathogen Causing Fruit Rot Of Trichosanthes Kirilowii Maxim And Screening Of Effective Fungicides

Trichosanthes kirilowii is an important local characteristic cash crop in China,which can be used in food,health care,medicine and other fields,and is loved by the majority of consumers.Trichosanthes kirilowii fruit rot is an important disease found on the fruits of Trichosanthes kirilowii.It causes fruit rot,reduces the yield of Trichosanthes kirilowii and affects the quality of Trichosanthes kirilowii.In recent years,the fruit rot of Trichosanthes kirilowii occurred in a large area in the producing area of Trichosanthes kirilowii in Dabie Mountains.In recent years,Trichosanthes kirilowii fruit rot is an important disease found on the fruits of Trichosanthes kirilowii,which leads to fruit rot,resulting in the reduction of Trichosanthes kirilowii yield and affecting the quality of Trichosanthes kirilowii.In this study,the pathogen of Trichosanthes kirilowii fruit rot was isolated and identified from the producing areas of Trichosanthes kirilowii in Daguan District,Qianshan County and Susong County of Anqing City,Anhui Province from 2019 to 2020,and the pathogenicity of different kinds of pathogens to Trichosanthes kirilowii fruit was explored,and the toxicity of seven commonly used fungicides to representative strains was determined.The main results are as follows:1.Isolation and identification of pathogenic.Fifty two pathogens were isolated from the diseased fruits of Trichosanthes kirilowii.According to the colony morphology and conidial characteristics of the isolated strains on PDA,they can be divided into Fusarium（type I and typeⅡ）and Colletotrichum（classⅢ,classⅣand class V）.The colony of Fusarium type I（11 strains）were pure white on the front,developed aerial hyphae and cotton flocculent.The colony of Fusarium typeⅡ（3 strains）were pure white on the front,developed aerial hyphae and twisted into bundles.The colony of Colletotrichum typeⅢ（14 strains）had gray front,dense aerial hyphae,cotton flocculent,and scattered orange conidia in the center.The colony of Colletotrichum typeⅣ（4 strains）was pink on the front,and the aerial hyphae were short hairy and undeveloped.The colony of Colletotrichum type V（20 strains）was gray black on the front,and the aerial hyphae were short and undeveloped.Based on the cluster analysis of TEF-1αgene sequence and morphological observation,the representative strains of two types of Fusarium were identified as F.fujikuroi（type I）and F.proliferatum（typeⅡ）.Based on the multi gene cluster analysis and morphological observation,the representative strains of two types of Colletotrichum were identified as C.fruiticola（typeⅢ,ITS、ACT、CAL、CHS-1、TUB2、GAPDH）,C.sojae（typeⅣ,ITS、ACT、CHS-1、TUB2、GAPDH）and C.lianningense（type V,ITS、ACT、TUB2、GAPDH）.2.Pathogenicity test of pathogens.The results of pathogenicity test showed that the representative strains of each strain had pathogenicity to Trichosanthes kirilowii fruit.The mycelium block and spore suspension of the tested strains were inoculated on the fruit of"wanlou 9"by acupuncture inoculation.The results showed that F.fujikuroi had the strongest pathogenicity（the size of lesion was 7.4 mm on 14 d,by spore suspension）,followed by C.fructicola,F.proliferatum,C.lianningense,and C.sojae had the weakest pathogenicity（the size of lesion was 4.8 mm on 14 d,by spore suspension）.Through the experiment of F.fujikuroi and C.fructicola,F.fujikuroi and C.lianningense complex infecting Trichosanthes kirilowii fruit.The results showed that the complex infection of F.fujikuroi and C.fructicola,F.fujikuroi and C.lianningense could cause the fruit rot of Trichosanthes kirilowii.The results showed that the disease rate was faster when Fusarium and Colletotrichum were inoculated at the same time,and the disease spot diameter of F.fujikuroi and C.fructicola was the largest（the size of lesion was 11.5 mm on 14 d）.3.Screening of effective fungicides.According to the results of pathogenicity test,seven representative strains of F.fujikuroi,C.fruiticola and C.lianningense were selected to determine the toxicity of seven commonly used fungicides to seven strains by mycelial growth rate method.The results showed that chlorpromazine and difenoconazole had better inhibitory effect on the mycelial growth of the tested strains,the EC₅₀ of chlorpromazine on the tested strains ranged from 0.0633 to 0.1718μg/m L,the EC₅₀ of difenoconazole on the tested strains ranged from 0.1046 to 0.6536μg/m L;azoxystrobin had poor inhibitory effect on test strains,the EC₅₀ of azoxystrobin on the tested strains ranged from 0.2274 to470.1402μg/m L,the difference of bacteriostatic effect was the largest among different strains.