Identification,population Dynamic Analysis And Indoor Bactericides Screening Of Potato Blackleg Bacteria

Potato blackleg caused by soft-rot bacteria belonging to Pectobacteriaceae is one of the most important bacterial diseases worldwide.Blackleg symptoms occurred at any time during the growing season,while tubers soft-rot symptoms occurred during storage and transport.In 2015,the National’s strategy of promoting potoato as the fourth staple food was officially proposed.In recent years,with increasingly expanding cultivated area of potato,the incidence and severity of potato blackleg increased significantly,which posed a serious threat to the development of potato industry.The present studies abroad have shown that numerous species,e.g.Pectobacterium atrosepticum,P.carotovorum,P.brasiliense,Dickeya solani and D.dianthicola,from Soft Rot Pectobacteriaceae can cause Potato Blackleg.Most of the related domestic researches,however,focused on the species of Pectobacterium atrosepticum.Therefore,this study aims to isolate,identify and characterize blackleg-causing bacteria in China,establish the survival and population dynamics of isoalated bacterial strains under different conditions,evaluate in vitro antibacterial activities of commonly used bactericides to isolated strains by using morphological and physiochemical method,pathogenicity test,as well as phylogenetic analysis on the basis of16S r DNA nucleotides sequence.The main research results are as follows:1.A total of 312 suspected diseased potato samples with blackleg symptoms were collected from two main potato production areas in China,Northern single crop zone and Southern winter crop zone.Ninety-five bacterial strains were isolated by dilution plating method,then subject to observation of morphological characteristics,colony PCR,physiological and biochemical determination,pathogenicity test,BIOLOG as well as phylogenetic analysis on the basis of 16S r DNA nucleotides sequence.Among them,40 strains were identified as Pectobacterium atrosepticum,34 strains were P.carotovorum,15 strains were P.brasiliense and 6 strains were P.polaris.2.We compared the survival and population dynamics of four representative strains of P.atrosepticum,P.carotovorum,P.brasiliense and P.polaris under different conditions.In water at 4℃,P.atrosepticum strain P2K1808,P.carotovorum strain P2K1902,P.brasiliense strain P2K1910 and P.polaris strain P2K1907 survived up to 260 days with population densities of more than 10⁴cfu·m L^-1.In soil at-20℃,P.carotovorum strain P2K1902 and P.brasiliense strain P2K1910survived 200 days with population densities of 10⁴cfu·g^-1soil,P.polaris strain P2K1907 survived 200 days with population densities of 10²cfu·g^-1soil,whereas P.atrosepticum strain P2K1808 survived no more than 80days.3.By employing disc diffusion and growth curve method,we evaluated the antibacterial activities of 9 commonly used bactericides on representative strains of four species of Pectobacterium with 72%streptomycin sulfate soluble powder as control.It is clear that there are obvious differences in the antibacterial effect of different bactericides on the four pathogenic bacteria.It was found that 0.3%tetramycin aqueous solution has a significant inhibitory on Pectobacterium atrosepticum,P.brasiliensis,P.carotovorum,and P.polaris.The EC₅₀was 8.375,12.761,9.986,8.675 mg·L^-1,respectively.The correlation coefficient R value was0.984,0.958,0.943 and 0.953,respectively.Followed by is the 3%benzisothiazolinone wettable powder.The EC₅₀was 18.450,36.083,33.425 and 37.408 mg·L^-1,respectively.The correlation coefficient R value was 0.888,0.982,0.959 and 0.986,respectively.