ISSR genetic diversity analysis of rose black spot pathogen

【Objective】 This study aimed to investigate the species composition,genetic diversity and phylogenetic relationships of the rose black spot pathogen in China,which could provide theoretical basis for resistance identification ofrose germplasm against black spot and disease control strategies. 【Method】 The pathogen of rose black spot were isolatedfrom 27 cities （counties） of 15 provinces （autonomous regions） in 7 regions of China,and the pathogen species were determined by amplified strain ITS sequence,and the pathogenicity was verified by Koch’s rule. The genetic diversity of thepathogens was studied using the ISSR molecular marker technology. The band data obtained by amplification was recorded as a 0-1 matrix,and the genetic diversity index and genetic distance were calculated using PopGene 32.0,and theunweighted pair group method with arithmetic mean（UPGMA） clustering analysis was performed using NTsys-pc 2.1. 【Result】 A total of 107 strains of pathogen were isolated,which could be divided into 27 populations according to differentcities（counties）. All 107 strains were identified as Marssonina rosae. Three primers for ISSR-PCR amplification wereidentified: UBC884,UBC885 and UBC886. These primers produced a total of 84 bands,all of which were polymorphic,indicating a polymorphism rate of 100%,thus demonstrating high polymorphism,and it was suitable for the amplificationof M. rosae. Genetic diversity analysis of 107 strains showed that the mean observed number of alleles （Na）,mean effective number of alleles （Ne）,mean Nei’s diversity index （H） and mean Shannon’s information index(I) were 1.3369,1.2431,0.1367,0.1993,respectively. Average genetic diversity （Ht） was 0.2827,average genetic diversity within population （Hs） was 0.1368,average coefficient of genetic differentiation （Gst） was 0.5163,and gene flow （Nm） was 0.4684.Based on UPGMA cluster analysis,the 107 M. rosae strains could be divided into 8 groups when the genetic coefficientwas 0.57. In groups Ⅰ-Ⅶ,strains from different regions were mixed with each other,while some strains in group VIIIwere grouped together based on their geographical location of cities（counties）. 【Conclusion】 The 107 M. rosae strainsfrom different geographical regions exhibit rich genetic diversity,low gene flow among populations,and high genetic differentiation. Moreover,there is no strong correlation between the genetic diversity of the strains and their geographical origin.