[Objective]The purpose of the study was to identify the resistance of different rose variety resources to powdery mildew and screen resistant varieties,so as to provide theoretical basis for the prevention and control of rose powdery mildew and the breeding of resistant rose varieties.[Method]In the main growth period(May,August and No-vember)of rose in Yunnan,the natural incidence and resistance of powdery mildew in 674 rose varieties in the resource nursery of the national forestry and grassland plant new variety Kunming test station(Songming)were investigated.Five plants were randomly selected from each variety to investigate the percentage of disease spots on the leaf surface,and the resistance was evaluated according to the disease index.The fresh disease samples of rose powdery mildew(SM)were col-lected from Grand Gala,and they were isolated and purified.The morphological characteristics were observed.The ge-nomic DNA of rose powdery mildew was extracted and amplified by PCR.The ITS sequence of rose powdery mildew was aligned with the BLAST homology of different powdery mildew pathogens by NCBI,and the phylogenetic evolutionary tree of different hosts of powdery mildew was constructed based on the sequence similarity.Then the pathogen of rose powdery mildew was inoculated back and the resistance of rose was identified after in vitro inoculation of pathogen.[Re-sult]The results of the survey on the natural resistance of 674 rose varieties in the field to powdery mildew in three sea-sons showed that there were 211 rose varieties that showed resistance in spring(May),of which 77 varieties were highly resistant,81 varieties were resistant,and 53 varieties were moderately resistant,accounting for 11.42%,12.02%,7.86%respectively.In summer(August),there were 129 rose varieties showing resistance,of which 6 varieties were highly re-sistant,25 varieties were resistant,and 98 varieties were moderately resistant,accounting for 0.89%,3.71%and 14.54%respectively.In autumn(November),there were 120 varieties of rose showing resistance,including 7 highly resistant va-rieties,53 resistant varieties and 60 moderately resistant varieties,accounting for 1.04%,7.86%and 8.90%respectively.The results of BLAST homologous alignment and phylogenetic evolutionary tree showed that the gene fragments of SM strain had more than 99%similarity with the genes of Podosphaera pannosa.The SM strain was most closely related to the powdery mildew pathogen AB525939.1(rosebush),DQ139429.1(rose)and KF571742.1(rose)from different re-gions.Rose powdery mildew pathogen had the characteristics of highly obligate parasitism.The results of artificial inocu-lation of isolated leaves of 18 rose varieties(3 varieties of each grade)showed that the results of artificial inoculation in vi-tro were consistent with the field resistance phenotype.[Conclusion]The field resistance of rose powdery mildew is mainly affected by genetics,and most of the tested rose variety resources are susceptible to powdery mildew.The resis-tance level of plants in spring in Yunnan is higher than that in summer and autumn.Six highly resistant varieties are screened out,including Autumn Pomegranate Flower,Ginger Syllabub,Golden Celebration,Purple Tiger,Bassino and Fenghua Rose,which can provide resistant germplasms for the exploration of powdery mildew resistance genes in rose and the cultivation of disease-resistant rose varieties.
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