Pathogen Population Composition Of Fragrant Pear Valsa Canker In Fragrant And Transcriptome Analysis Of Dominant Species Cytospora Pyri

Fragrant pear industry is an important component of Xinjiang’s characteristic forest and fruit industry.For a long time,pear valsa canker has been prevalent in the main production areas of fragrant pears,causing weakened tree vigor,reduced yield,and decreased quality,posing a serious threat to the development of Xinjiang’s characteristic forest and fruit industry.In this study,infected tissues were collected from the main production areas of fragrant pear for identifying the pathogenic species and dominant pathogenic species using morphological analysis,multi-gene sequence analysis and pathogenicity determination.The dominant species were identified as Cytospora pyri,and its pathogenicity differentiation,genetic diversity and transcriptome analysis were conducted.The results provide a theoretical basis and Valsa canker control of fragrant pear.The main results are summarized as follows:1.Study on the population composition and biological characteristics of the pear valsa canker in different planting areas.A total of 423 monosporal pathogenic strains of Cytospora spp were isolated and purified from 16 cities and counties in the main pear producing areas.According to the differences of potato dextrose agar(PDA)culture characteristics,the strains were categorized into 10 groups,in which 48 representative strains were selected based on the results of ITS identification.Multi-locus analysis(internal transcribed spacer,translation elongation factor 1-alpha,beta-tubulin)and morphological observation showed that the pathogens were C.pyri,C.chrysosperma,C.mali and C.nivea which belong to the four species of Cytospora.91.73%(388 strains)of the total 423 strains were C.pyri,which were the dominant population of the canker pathogens that were widely distributed in the plantation areas for fragrant pear in Bazhou,Aksu and Kashgar region.C.nivea was a newly recorded species.The study examined the biological traits of four different species.The results indicated that the environmental factor for the four species of were different,and there were differences in their pathogenicity to different hosts,among which C.pyri and C.mali had strong pathogenicity to Pyrus sinkiangensis and Malus domestica,respectively,while C.chrysosperma had strong pathogenicity to Juglans regia,Populus alba and Salix matsudana.C.nivea was weakly pathogenic to all tested hosts.The virulence of seven canker-causing agents from various hosts towards fragrant pear demonstrated that C.pyri from apple trees was more pathogenic to fragrant pears than C.chrysosperma from Populus euphratica Oliv..However,C.leucostoma from almond and C.euonymina and Cryptosphaeria pullmanensis from Populus euphratica Oliv.were not pathogenic to Pyrus sinkiangensis.These results indicated that cross-infection could occur in different hosts,but canker pathogens obtained from different host sources exhibit stronger pathogenicity on their original hosts than on other hosts.2.Pathogenic differentiation and genetic diversity analysis of C.pyri from fragrant pear treeThe pathogenicity of 50 strains of C.pyri from three fragrant pear growing areas,including Bazhou,Aksu and Kashgar,was determined.The results showed that among the 50 C.pyri strains,strong,medium,and weak pathogenic strains accounted for 10%,82%,and 8%,respectively.There were significant differences in the pathogenicity from different plantation areas,with ALE2 having the largest spot diameter after inoculation,indicating a strong pathogenicity strain,and XH1 having the smallest plaque diameter,indicating a weak pathogenicity strain.The genetic diversitys of C.pyri were analyzed by molecular marker techniques.The results showed that the percentage of polymorphic bands was 90.38% among eight geographical populations.The high Nei Shannon Information Index(0.4024)of the pathogen indicated its rich genetic diversity within its populations,which was a sign that C.pyri had accumulated a high level of genetic variation during its long evolutionary history.The genetic diversity within the geographical population accounted for 86.74% of the total population diversity,and the variety inside the population surpassed the one between populations.This indicated that the genetic variation of C.pyri in Xinjiang was mainly within the population.Based on the genetic differentiation coefficient,a gene flow value was determined,and it was larger than 1,indicating that there was substantial genetic exchange between groups.UPGMA clustering results showed that each geographical population was correlated with distance to some extent,and there was gene flow between different geographical populations.The genetic relationship between C.pyri populations was found to be correlated with their geographical origin.3.Transcriptome analysis of pear branches infected by C.pyriThe transcriptomes of branch tissue infested by strong pathogenic strain ALE2 and weak pathogenic strain XH1 were sequenced and analysed.388 differentially expressed genes were obtained.Analysis of differentially expressed genes revealed that many amino acid metabolic pathways and pentose-glucuronide interconversion pathways were significantly enriched during C.pyri infestation,and strong pathogenic strains were significantly enriched in pathways such as nutrient acquisition,cell wall degrading enzymes,and maintenance of their own structure.The enrichment was presumably related to pathogenicity.10 hub genes were found by analyzing the PPI network of DEGs,,among which VP1G＿01947 and others were involved in GPI anchor biosynthesis and core oligosaccharide synthesis process,and VP1G＿07986,VP1G＿06927 and VP1G＿00485 were involved in cell wall hydrolysis process.