Occurrence Dynamics,variety Resistance And Screening Of Indoor Control Chemicals Of Colletotrichum Salicis On Cherry Leaf Spot In Qinghai Province

The sweet cherry planting area in Qinghai Province is mainly concentrated in the Huangshui River basin and the Yellow River basin in the Chuanzhong plain area and the loess hilly shallow mountain area,where the temperature is suitable,the light is sufficient,and the annual rainfall is over 400 mm,which is suitable for high yield cherry cultivation.In recent years,due to rising temperature,increased rainfall,rapid propagation of pathogenic bacteria,improper management of orchard cultivation,and incomplete control of diseases and insect pests,the diseases on cherries have increased significantly,especially leaf spot disease,which is the most common,and has caused huge economic losses and serious impacts.Healthy development of the cherry industry.At present,there are few reports on the disease at home and abroad.On the basis of previous research,this paper systematically studies the dynamic law of occurrence of cherry leaf spot in Qinghai Province and the characteristics of the culture environment of the main pathogenic bacteria.In addition,the disease resistance of 28 varieties imported from abroad was evaluated,and the indoor virulence of 32 fungicides was determined.The main results are as follows:1 Epidemic Dynamics of Cherry Leaf Spot Five point sampling method was used to systematically investigate and statistically analyze the occurrence and harm,epidemic time dynamics and main meteorological factors of cherry leaf spot in Qinghai Province.The results show that the seasonal epidemic curve of the disease is a typical single peak S-shape,showing the characteristics of gentle in the early stage,rapid outbreak and stable in the later stage,and according to the analysis of epidemic model,logistic model is the best model to predict the epidemic time dynamics of diseases.According to logistic formula,the disease stages are divided into:the exponential growth period is from early June to the end of July;The logistic period is from the end of July to the first ten days of September;The recession period is in early September and beyond.In addition,the logistic prediction model of disease condition and main meteorological factors was constructed for the first time.Combined with the epidemic time dynamics of the disease and meteorological factors,the chemical prevention period and key control period of cherry leaf spot were put forward.The prevention period is 6 months before the disease occurs;the key control period is from early June to the end of July,and since June 1,the accumulated temperature has not reached941.2℃,the accumulated relative humidity has not reached 3546.3%,the accumulated sunshine hours have not reached 475.1 h and the accumulated rainfall has not exceeded186.0 mm.2 Biological characteristics of pathogenic bacteria The mycelial growth rate method and spore count method were used to study the effects of different culture conditions on the growth and spore production of the main pathogen C salicis.The experimental results showed that the optimal medium for mycelial growth and sporulation of pathogenic bacteria was PDA medium.Results indicated that the optimal carbon sources for colony growth and sporulation were inositol and glucose.The optimal nitrogen sources for colony growth and spore production were beef extract and peptone.All pathogens could grow at a temperature of 5℃to 40℃and develop fast at a temperature of 25℃.However,when the temperature as high as 58℃and incubating for 10 min,pathogens died.The pathogenic bacteria could grow and sporulation in the p H range of 4 to 12,and the optimum p H value is 7 to 8.Under 12 h/12 h alternating light and dark,the colony grew fast and sporulation was more.3 Evaluation of disease resistance of different sweet cherry varieties against pathogen The study was conducted using 28 cherry resource varieties imported from Qinghai Province as experimental materials,using the methods of indoor isolated leaf inoculation and field live leaf inoculation.The variety provides a theoretical basis for the selection and breeding of leaf spot resistant varieties in Qinghai Province.The results showed that the inoculation results of isolated leaves in the room and the live leaves in the field were highly consistent with the cluster analysis using Wald’s method and Euclidean distance.Among the 28 sweet cherry cultivars,Early Robin,Lambert,and Moreau were the stronger resistances of cherry cultivars,while the lower resistances of cherry cultivars were Rainier,Tieton,Sunburst,and Hongdeng.4 Screening of fungicides for pathogen in laboratory Taking C.salicis as the research object,the mycelial growth inhibition method and detached leaf inoculation method was used to measure the virulence of 32 fungicides in the laboratory.The results showed that among the tested fungicides,10%phentermine methiconazole aqueous dispersion and 0.3%eugenol dissolvable solution had the greatest inhibition effect with EC₅₀ values of 0.6 mg·L^-1 and 1.151 mg·L^-1,respectively.The inhibition effect of 20%ethyl allantoin EC,80%daidzein WP,and 500 g/L isoxuron SC was poor,with EC₅₀values as high as 301.44 mg·L^-1,679.36 mg·L^-1,and 1012.52 mg·L^-1.In addition,among the six bio-control reagents,multianthemycin soluble granules and Trichoderma elongate powder had the best inhibition effect.And the best spraying time of multianthemycin is 2 or 3 days before inoculation,and Trichoderma elongate is 2 days after inoculation.Followed by pythium oligadrum wettable powder,Trichoderma harzianum wettable powder,and Bacillus subtilis wettable powder,and the worst inhibition effect was Wuyiencin aqueous agent.