Genetic Diversity And Variation Analysis Of Pseudomonas Syringae Pv.actinidiae Isolated From Main Kiwifruit Producing Areas In Sichuan Province

Kiwifruit canker is a bacterial disease that seriously damages the growth of kiwifruit.Its main pathogen is Pseudomonas syringae pv.actinidiae(Psa).Due to the variation of pathogenic bacteria,genetic exchanges between each other,influences of the external environment and interactions between the host and other factors,the genetic information of pathogenic bacteria changes,making the epidemic and control of the disease more complicated.As a major province for kiwifruit cultivation,Sichuan Province is facing a situation ofmore prevalent and widespread disease.This study aimed to isolate and identify PSA in the main kiwifruit production region,and then to study its genetic diversity.The main conclusions are as follows:(1)For the first time,142 samples of suspected kiwifruit canker were collected from the main production areas of kiwifruit,includingGuangyuan,Chengdu,Chongqing,and Ya’an.77 Psa strains and 3 pseudomonas strains(Pseudomonas)wereacquired by identifying through isolation and culture.There are subtle differences in the morphology of pathogens.(2)Analysis of genetic diversity of 80 strains by BOX-PCR and EIRC-PCR.A total of 24 specific bands were amplified by BOX-PCR,the polymorphism rate was 96%,and 19 specific bands were amplified by ERIC-PCR.The polymorphism rate was 94.7%.The two methods classify 80 strains into 6 categories,showing a certain correlation with the geographical distribution of the strains.(3)Analysis of single nucleotide polymorphisms in 11 VNTR loci showed that 1 was a slight variation site,5 were moderate variation sites,and 5 were high variation sites.Similarity coefficient is 0.778,the method can aggregate 80 strains into 7 clusters,and the clustering results have a certain correlation with the geographical distribution of the strains and host species.(4)Through the analysis of the three housekeeping genes gapA,gyrB,pfk,the natural selection pressures of different gene segments are different.For Sichuan population,gapA,gyrB gene segments are positive selection,and pfk gene is negative selection.Within the Sichuan population,the Guangyuan population had frequent genetic exchanges with Chengdu,Leshan,and other local groups,indicating that the pathogenic bacteria population of Guangyuan was the source of the Sichuan population.(5)By measuring the pathogenicity of representative strains,the results showed that all the strains were pathological.Three strains of Pseudomonas are moderately pathogenic.The pathogenicity of the strain CX79.1.1 isolated from Cangxi of Guangyuan was extremely strong,and the strain AB62.8 isolated from Aba State was highly pathogenic.Most of the strains with large variations were weakly pathogenic and a few strains were moderately pathogenic.