Pathogenicity Differentiation For Valsa Pyri And Indoor Screening Of Fungicide

The pear varieties cultivated in different pear producing areas in China are different,and the incidence of Valsa canker is also different.In this study,the biological characteristics of strains from different sources and the differentiation analysis of pathogenic properties of strains from different sources were carried out by using the strains obtained and the strains isolated from Pyrus sinkiangensis,P.communis,P.ussuriensis,P.pyrifolia and Malus pumila in the early stage of this experiment as materials.It aims to provide a new experimental basis for the research and development of effective prevention and control technology of pear Valsa canker.The results obtained are as follows:1.A total of 43 Valsa strains were obtained according to the morphological characteristics of the colonies,and the results of further genetic phylogenetic analysis showed that the isolated Valsa strains all belonged to Valsa pyri,the symptoms produced by inoculation of mycelial blocks representing the strain on live P.betulaefolia seedlings were consistent with their field performance.The results showed that Xinjiang pear strains were the same pathogen as P.bretschneideri pear Valsa canker cultivated in the north of China,the P.pyrifolia pear Valsa canker strains cultivated in the south and the Pyrus communis pear Valsa canker strains cultivated abroad,but different from the apple strains,the former belong to Valsa pyri,and the latter belong to Valsa mali.2.In this study,morphological and phylogenetic analysis of strains isolated from Korla pear in Xinjiang and strains isolated from other four pear species in the early stage of this experiment showed that the colony morphology of pear strains was different from that of apple strains,and the concentric wheel rings of the latter colonies were more obvious and the hyphae were denser.Most strains of pear have milky white colonies,and only strain derived from P.bretschneideri produce yellow pigments.The stroma of strains derived from different pear species also differs.The results of polygenic phylogenetic results showed that the strains derived from the five pear species were clustered in one branch with the representative strain of Valsa pyri,while the apple strain was clustered in another branch with the representative strain of Valsa mali.The results of inoculation of different germplasm-derived strains into ex vivo shoots of different pear cultivars showed that the pathogenicity of pear strains was significantly stronger than that of apple strains.The results of inoculation of the strains derived from 5pear germplasm into different pear varieties showed that the strains derived from P.bretschneideri were more pathogenic than the other pear species,while the strains derived from the five pear germplasm were mostly moderately virulent,accounting for more than60%,but there were differences in the proportion of strong and weak strains,the proportion of strong pathogenic strains from P.pyrifolia（28%）and the proportion of weak pathogenic strains from P.ussuriensis（16%）higher than the source of other pear germplasm.3.The results of the inhibition determination of Valsa pyri by chemical agents showed that mycelial growth was sensitive to four agents:manganese zinc,allicin,nymazole and fluorohydroxybenzazole,and the EC₅₀value was less than 0.3μg/ml.Conidia germination was more sensitive to manganese zinc and imazole,and their EC₅₀values were lower than 0.2μg/ml.The effect of the above agents on pear rot disease shows that the protective effect of manganese zinc,pyraclostrobin and nymazole is more than 70%,while the therapeutic effect of pyraclostrobin,inhibidazole and azolyl fluranamide is more than 75%.