Study On Biological Characteristics And Identification Of Canker Pathogens On A Few Trees

Bark canker is a very serious disease on many kinds of trees, it causes dieback of twigs and branches, reduces tree growth, affects lumber quality, and causes significant yield losses on fruit trees. The species of canker pathogens are complex and the host range are extensive, the canker disease control meets a difficult problem under such conditions. Morphological identification and classification of canker pathogens are influenced by host and all kinds of environmental factors. Molecular identification based on ITS sequences can make an assay of canker pathogens on the level of gene and avert the environmental affected. It is widely used in the identification, classification and phylogenetic analysis of fungus.The pathogens of barker canker diseases on the eleven different kinds of trees were isolated and their pathogenicity were evaluated. The species identity of the pathogen of canker was determined through rDNA-ITS sequences analysis with homological sequences in GenBank and morphological feature. In addition, the sensitivity to the four fungicides (propiconazole, ambam, difenconazole and saimeitong) of canker pathogens were also evaluated. The main results are as follows:1. Phylogenetic analysis and morphological identification showed that the pathogens of canker on eleven trees are Valsa mali var. mali, Valsa sordida, Leucostoma persoonii, Phomopsis eucommicola, Botryosphaeri dothidea, Botryosphaeria rhodina and five species of Phomopsis spp. respectively. The group based on quantity of aerial hypha on PDA culture medium and the clade of phylogenetic analysis are identical, and the pathogens can not form fruiting body and conidiophores on PDA culture medium except the Phomopsis species.2. First report six species of Phomopsis spp. on five kinds of hosts in Hebei province. Because of the imperfection of the taxonomy system, we could identify Phomopsis eucommicola only, and the specise of other Phomopsis spp. pathogens needs further studies.3. Through the informations of homologous sequences in GenBank, we can know that the geographical origin of canker pathogens is widely, and the pathogens do not to express specialization of hosts except Valsa mali, Valsa mali should be in a process of hosts specialization.The pathogens do not to express widely difference during suitabilities of temperatures, pH values and culture mediums neither, as a result the geographical origin and condition of environment do not cause the phylogenetic division of canker pathogens.4. The sensitivities to four fungicides of canker pathogens were assayed and the results showed that all tested isolates were sensitive to propiconazole and difenconazole. The mean values of effective concentration (EC50) among the isolates were under 0.5μg/mL and 0.1μg/mL, respectively. The tested isolates were not sensitive to ambam and saimeitong obvious.