Collection And Characteristics Primary Research Of Peronophythora Litchi Strains

Peronophythora litchii is one of the most serious diseases for litchi,because it cannot only cause the flower-and fruit-drop and fruit browning before harvest,but shorten the shelf-life of postharvest fruit;further reduce the fruit production and commerce value.Collecting the genetic resources of P.litchii and evaluating their characteristics,such as pathogenicity,would provide the basisforstudying the pathogenic mechanism and developing the effective prevention and control technology.In this study,some P.litchii strains were collected from several litchi production areas,then several biological characters of P.litchii were evaluated.The difference of pathogenicity to litchi fruits among the P.litchii strains were tested,and their genetic diversities were detected by RAPD,ISSR markers and 18S-rDNA sequence analysis.The main results were as followings:1 A total of 32 single spore strains of P.litchii were isolated from disease samples obtained from orchards located at Huidong,Zhanjiang,Zhangpu and Haikou.Some biological characters of P.litchii were evaluated using HNYF strain as an example.The strain showed various growth statuses on different medium.The strain had sparse,annular hypha growth on 10%V8 medium,with the highest spore-bearing rate.When it was grown on 5%V8 medium,the strain had the highest hypha growth rate and lower spore-bearing rate than that on 10%V8 medium.It had the lowest spore yield on PDA medium.The hypha could grow under the temperature from 16 ℃ to 32 ℃ and the pH value from 4.0 to 9.0,with the highest growth rate under temperature at 24 ℃and pH value at 7.0,respectively.It has the largest spore yield under the condition of light-darkness alternation.2 The pathogenicities of the 32 P.litchii strains to ’Shuanjianyuhebao’ litchi fruit were evaluated.The HD1-10 was the highest pathogenic strain,and the HD2-8 was the lowest one.The pathogenicity had little relationship with the origin of the P.litchi strain,whether the location or the litchi cultivars.HD2-8 had a relatively lower hypha growth rate and spore yield rate than HD 1-10.3 The genetic diversities of the 32 P.litchi strains were detected by RAPD and ISSR markers and 18S-rDNA sequence analysis;however,few variations were found.According to the results of RAPD and ISSR markers,the 32 P.litchi strains were classified into three groups,roughly corresponding to the geographical origin of the strains.However,the classification had little relationship with the original litchi cultivar and pathogenicity of the P.litchi strains.There were few differences among the 18S-rDNA sequences of 32 P.litchii strains.4 The inhibitory effects of six compounds extracted from plant,i.e.,artemether,dihydroartemisinin,artesunate,fructuscnidii,capsaicin and magnolol,on the hypha growth of the 32 P.litchii strains were tested.All the compounds could inhibit the hypha growth,among which the magnolol had the best inhibitory effects with the EC50 value at 31.20 μg/mL,following by dihydroartemisinin,with the EC50 value at 60.00 μg/mL.The other four compounds showed lower inhibition on the hypha growth.Artemether had the highest EC50 value at 139.30 μg/mL.