Identification Of The Pathogens Causing Cherry Leaf Spot In Qinghai Province And Screening Fungicides In Laboratory

The cherry planting areas in Qinghai province are mainly concentrated in the Huangshui river basin below the altitude of 2200 m and the plains and rivers in the Yellow river valley and the shallow hills of the loess hills.Here the temperature is suitable,the light is sufficient,and the annual rainfall is 400～500 mm,which is suitable for the high-yielding cultivation of cherries and the growth of microorganisms.In recent years,due to temperature rises in Qinghai province,increased rainfall,rapid propagation of the pathogens,coupled with improper orchard management and incomplete control of diseases and insect pests,the incidence of diseases on cherry has increased significantly,especially leaf spot occurs most commonly and causes large losses,which seriously affects the healthy development of the cherry industry in Qinghai province.At present,there are few studies on the disease at home and abroad and it has not been reported in Qinghai.Therefore,this study isolated and identified the pathogens and studied the biological characteristics of the main pathogen.On this basis,the indoor disease resistance of 38 imported varieties in the United States was evaluated,and the virulence determination of the main pathogen was determined with a single agent of 9 kinds of fungicides.The main research results are as follows:1 Identification of the pathogens causing cherry leaf spot The cherry leaves with typical leaf spot symptoms were collected from Chengbei district of Xining city,Ledu district of Haidong city,and Guide county of Hainan state.The pathogens were isolated using tissue isolation technology.By observing the morphological characteristics of the pathogens,combined with multi-gene sequence analysis.Finally,the pathogens of cherry leaf spot in Qinghai province were identified as Alternaria alternate,A.tenuissima and Colletotrichum salicis,and the isolation frequencies were 84.95%,5.02% and 10.03%,respectively.2 Study on biological characteristics of pathogen 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 A.alternata.The results showed that the optimal medium for mycelium growth and spore production was PSA medium and PDA medium,respectively.The optimal temperature was 25℃,the optimal nitrogen source was peptone,The optimal carbon source was inositol and lactose,and the optimal p H was 6～8 and 6～7,respectively.24 h dark treatment was more favorable for mycelium growth and sporulation.3 Evaluation of disease resistance of different cherry varieties against pathogen The disease resistance evaluation of 38 imported varieties in the United States was carried out by using inoculated leaves in vitro.The results showed that there were 24 varieties with strong resistance to A.alternata,accounting for 63.16% of the total varieties.4 Screening of fungicides for pathogen in laboratory Taking A.alternata as the research object,the mycelial growth inhibition method was used to measure toxicity of 9 fungicides in laboratory.The results showed that nine kinds of chemical agents have different degrees of inhibition on the pathogen.Among them,250 g/L Azoxystrobin SC has the best antibacterial effect,and the EC₅₀ is 1.258 mg/L.