| Pear is major fruit trees in china, which plays an important role in improving people's life quality and promoting China's economic development. Pear black spot is one of the major diseases of pear, which harms leaves, fruits and young shoots, weakens the trees. It causes serious economic losses to the pear industry, and restricts the development of pear industry. The etiology of pear black spot was studied based on isolation and identification of pear black spot pathogen from Hubei province sand pear producing areas and the germplasm bank of Wu Chang Sand Pear Garden National Fruit-tree Germplasm Resources; High disease resistant germplasm of sand pear were screened by assessment of sand pear germplasm resistance to pear black spot;The candidate resistance genes of sand pear to the pear black spot were identified and defense mechanism of sand pear to the black spot was studied by transcriptome sequencing of high resistant pear germplasm and high susceptible pear germplasm; The study lays a theoretical foundation for prevention and treatment of the pear black spot disease and molecular breeding. The main research results were as follows:1.474 strains were obtained based on isolation and identification of pear pear black spot pathogen from Hubei province sand pear producing areas and the germplasm bank of Wu Chang Sand Pear Garden National Fruit-tree Germplasm Resources(WCSPGNFG).According to the degree of color of colony, the colors of the pear black spot pathogen strains were divided into light grey Telegrau 4, grey Platingrau, light green-brown Betongrau, light green-brown Quarzgrau, dark grey Zeltgrauu and dark brown Betongrau; Variation range of average daily growth rate of strains was 0.4cm/d-1.28cm/d; Variation of sporulation quantity was 104-1.01×107 cfu/ml; 108 pathogenic type were obtained based on 152 strains inoculated with "Jinjing pear" "Hongfen pear", "Xiangnan ", "Huangjin", "Shao Tongxiao Huang Li", "Housui", "Cuiguan", "Yunlu", and "gold Nijisseiki";The results of 50 strains sequence analysis by ITS, EF1-?,?-tubulinDNA molecular markers showed pear black spot dominant strains which infected the producing area pear of Hubei province were Alternaria alternata (Fr.) keissl, and had no significant difference with the standard strain CBS in these three markers.2.In this study,331 sand pear germplasm from the germplasm bank of WCSPGNFG were evaluated for their resistance to the black spot under artificial inoculation conditions. Results showed that, nine sand pear varieties were highly resistant to A. alternata,71 were resistant,165 were moderately resistant,68 were susceptible and 18 were highly susceptible to the black spot.The results will lay the foundation for resistance gene discovery and breeding for sand pear resistant.3. To investigate the defense mechanisms of sand pear in response to the black spot, the transcriptome of "Jingjing pear" which was high resistance to black spot and "Hongfen pear" which was high susceptible to black spot were analyzed using Illumina paired-end sequencing. In total,20.5 Gbp of sequence data and 101,632,565 reads were generated, representing 44717 genes. Approximately 66% of the genes or sequenced reads could be aligned to the pear reference genome. A large number (5213) of differentially expressed genes related to PBS resistance were obtained; 34 microsatellites were detected in these genes, and 28 genes were found to be closely related to PBS resistance. Using a transcriptome analysis in response to PBS inoculation and comparison analysis to the PHI database,4 genes (Pbr039001, Pbr001627, Pbr025080 and Pbr023112) were considered to be promising candidate for sand pear resistance to PBS. This study provides insight into changes in the transcriptome of sand pear in response to PBS infection, and the findings have improved our understanding of the resistance mechanism of sand pear to PBSand will facilitate future gene discovery and functional genome studies of sand pear. |
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