Pathogenicity Differentiation Of Colletotrichum Fructicola From Main Pear Producing Areas In South China And Laboratory Test For Resistance Of Pear Variety

In recent years,the early defoliation on pear and abnormal flowering occurred in autumn in southern China.The disease resulted in large losses in pear yield and quality,and there is an increasingly urgent need to solve this problem in production.In our laboratory,it was confirmed that the main pathogen of Colletotrichum fructicola was causing this disease.In this study,the aims are to establish the laboratory determining methods of pathogenicity to he pathogens C.fruticola,analyze the pathogenicity differentiation for the pathogen of C.fructicola from different sources and determine the laboratory resistance of pear varieties of Pyrus pyrifolia and P.bretschneideri to the pathogen,which laid a foundation for further study on the pathogenic mechanism of C.fructicola,and provide a basis for the selection and the application of pear varieties resistant to anthracnose.The results were as follows:1.The mycelial plugs and conidial suspensions of the strong pathogenicity strain PAFQ32 of C.fructicola were inoculated on the detached twigs(P.pyrifolia cv.Cuiguan),leaves(P.pyrifolia cv.Cuiguan),and fruits(P.bretschneideri cv.Huangguan)of pear after the wounds were caused by various methods,and according to the severity and stability of each treatment as the evaluation standard of the determining method.The results of laboratory determining methods of virulence showed that,on inoculated leaves,the expansion speed of the lesions produced by inoculated mycelial plugs was faster than that inoculated conidial suspensions,the disease incidences of inoculated mycelial plugs was 100% by each treatment,and the average diameters of lesions caused produced by puncturing 3 needles were significantly larger than 1 needle on the right side of leaves,and the incidence is stable;on inoculated fruits,the average diameters of lesions caused by inoculating mycelium plugs with each treatment were larger than conidial suspensions,but there was no significant difference among lesions sizes produced by inoculating mycelial plugs with different treatments;on inoculated twigs with mycelial plugs,the disease incidences of the twigs wounded by five methods were,respectively,80% by girding,40% by puncturing 10 needles,20% by puncturing 3 needles,100% by holing and scald holing.The average diameters of lesions treated with scald holing was significantly larger than other treatments,but the incidence was unstable.The results showed that the effect of determining the treatment of inoculating mycelial plugs by puncturing 3 needles on the right side of pear leaves was rapid and stable,so it can be used for rapid determination of the pathogenicity of the pathogens C.fruticola.2.Taking the detached leaves(P.pyrifolia cv.Cuiguan)of pear as inoculatedmaterials,111 strains of C.fructicola were isolated from 7 pear producing areas(Anhui,Fujian,Guangxi,Hubei,Jiangsu,Jiangxi,and Zhejiang)were determined by the method of puncturing 3 needles on the right side of pear leaves with mycelium plugs.The results showed that through the cluster analysis of the average diameters of lesions produced after inoculation,the strains could be divided into three types including 17 strains with strong pathogenicity(15.3%),89 strains with middle pathogenicity(80.2%)and 5 strains with weak pathogenicity(4.5%).There were significant differences in the proportions of the pathogenic types of the strains from different areas.The results showed that there was significant pathogenicity differentiation of C.fructicola causing early defoliation of pear in southern China,and the strains with middle pathogenicity were the dominant group.3.The laboratory resistance of 76 pear varieties of P.pyrifolia and P.bretschneider were determined by inoculating the mycelial plugs of the strong pathogenicity strains PAFQ32 and ZJHZ-7-1 of C.fructicola on the leaves after the wound was caused by puncturing.The results showed that through the cluster analysis of the average diameters of lesions produced after inoculation,the resistance of 76 pear varieties could be divided into five types including 4 pear varieties with highly resistant(5.3%),26 pear varieties with resistant(34.2%),25 pear varieties with moderately(32.9%),17 pear varieties with susceptible(22.3%)and 4 pear varieties with highly susceptible(5.3%).The results showed that belong to the high-resistance grade cultivars were P.pyrifolia,so the P.pyrifolia should be the key selection object in the pathogen C.fruticola-resistance screening.