Biological Characteristics Of Corynespora Cassiicola And Screening Of Fungicides In Laboratory

Fengxin County is a large kiwifruit planting county in Jiangxi Province,and kiwifruit industry plays an important role in promoting local economic development.However,in recent years,with the continuous expansion of kiwifruit’s planting scale in this area,Corynespora cassiicola,which has a serious impact on the yield and quality of kiwifruit,is also increasing.In order to provide theoretical basis for comprehensive management of this plant disease,this article launched the research of the field investigation of diseases,the determination of biological characteristics of pathogenic fungus,the screening of disease-resistant varieties,and the indoor screening of biocontrol agents and chemicals.The research results are as follows:Field investigation of Corynespora leaf spot of kiwifruit（variety Hongyang）in Shankou planting base was carried out at the intervals of 15-20d from May to November in 2019.500leaves of kiwifruit were randomly collected,and the leaves were graded according to the established grading standard,and the disease index was calculated.The results showed that the initial onset of the disease occurred around May 15,with a lower disease index of 3.56,and the peak onset occurred around August 15,when the disease index reached 59.68.In September,the disease resulted in serious defoliation,and the non defoliated leaves also had a lot of disease spots.In the next year,a field investigation of the disease on 20 varieties of kiwifruit in the base of Shankou was conducted using previously described method.The results showed that among the 20 varieties,one was highly susceptible,two susceptible,seven resistant,nine highly resistant and one immune.Studies on the biological characteristics of C.cassiicola indcated that the optimum growth temperature and spore germination temperature were both 30℃.The optimum growth p H value was 6.The 24-hour light condition was most beneficial to the growth of pathogenic fungus.PDA was the optimum growth medium.Mannitol and potassium nitrate were the optimum carbon and nitrogen sources.In the resistance identification test of kiwifruit varieties to Corynespora leaf spot,the detached leaves of 20 varieties and 15 varieties were inoculated with the PDA-cultured fungus cake and with the spore suspension prepared from PCA culture respectively,and the resistance types of varieties were classified according to the severity of disease.The results showed that the two inoculation methods led to two different identification results.Among20 varieties inoculated with the fungus cake,five varieties showed highly susceptible,six susceptible,six resistant and three highly resistant,while among 15 varieties inoculated with the spore suspension,two varieties showed highly susceptible,one susceptible,four resistant,two highly resistant and six immune.In contrast,the results of the latter method can better reflect the actual resistance of a variety.A biocontrol strain in Bacillus obtained in the early stage and nine commercial biocontrol agents were selected for indoor bacteriostatic experiments on C.cassiicola.The results showed that Bacillus subtilis had the best bacteriostatic effect with the bacteriostatic rate as high as 72.73%.The next ones were Bacillus amyloliquefaciens,Bacillus simsii,Pseudomonas fluorescens,Bacillus licheniformis,Bacillus megaterium,Bacillus cereus,Bacillus laterosporus and Trichoderma harzianum with the bacteriostatic rate ranging from33.17%to 66.87%.Aspergillus oryzae had the worst bacteriostatic effect with the bacteriostatic rate of only 30.94%.In the indoor toxicity test of 17 fungicides to C.cassiicola.The results showed that 50%Prochloraz Manganese chloride complex WP,50%Difenoconazole Propiconazole EC,40%Flusilazole EC and 50%Fluazinam SC had strong toxicity,and the EC₅₀ values were 0.157,0.574,0.740 and 0.783μg/m L respectively,all less than 1μg/m L.The other fungicides were 75%Trifloxystrobin Tebuconazole WG,75%Tebuconazole Azoxystrobin WG,19%Picoxystrobin Propiconazole SC,43%Tebuconazole SC,12%Zhongshengmycin WP and60%Pyraclostrobin Metiram WG,and their EC₅₀ values were in the range of 1～10μg/m L.The toxicity of 50%Iprodione SC,40%Pyrimidine SC,80%Ethylicin WP and 80%Thiram WG were all weak,and their EC₅₀ values were all greater than 28μg/m L.