Diversity Analysis Of Potato Common Scab Pathogens And Disease-resistant Germplasm Screening

Solanum tuberosum L.is the fourth largest food crop in the world and an important agricultural product for Chinese farmers to increase their income.Potato common scab is a soil-borne and seed-borne disease caused by pathogenic Streptomyces,which occurs widely in potato growing areas all over the world.The disease mainly affects the potato tubers,destroys the epidermis of potato tubers,and influences the economic value of potato.In recent years,it has been a growing trend for the occurrence of potato common scab in Chinese potato production areas.The diversity of potato common scab pathogens and the lack of potato resources with high resistance to scab are the main factors restricting the control process of potato common scab.In this study,we collected potatoes with potato common scab from 22 areas in 20 provinces of China,counted the types of scab spots,isolated and purified the pathogens from the scab lesions,and detected the pathogenic genes of the obtained strains and identified the genetic composition of pathogenicity islands(PAI).And the pathogenicity of Streptomyces were verified by small potato chip method,radish seedling method and pot experiment.And the Streptomyces were identified by molecular biology and morphology.Then the control efficacy of the two fungicides on potato common scab were evaluated through pharmaceutical treatment.Finally we identified the disease resistance of potato germplasm resources through field experiments,and screened the resistant resources.The main results are as follows:1.In this experiment,we collected potato common scab samples from 22 regions in20 provinces of China,and counted the types of lesions.The results showed that there were three types of lesions,including the convex,concave and flat lesions,of which concave and flat lesions were mostly common,while convex lesions were relatively rare.2.We isolated and purified pathogenic bacteria of the collected potato common scab samples and 34 strains of Streptomyces spp.were identified.Molecular identification and cluster analysis of the tested strains showed that there were 10 species of Streptomyces sp.isolated from the samples.Including of Streptomyces scabies,Streptomyces europaeiscabiei,Streptomyces diastatochromogenes,Streptomyces turgidiscabies,Streptomyces caviscabies,Streptomyces galilaeus,Streptomyces bobili,Streptomyces acidiscabies,Streptomyces enissocaesilis,Streptomyces griseus.Among which Streptomyces scabies is the dominant strain,which distributing in 6 different regions,followed by Streptomyces bobili,which distributing in 3 different regions.3.Detecting the pathogenicity-related genes(txt AB,tom A,nec1)of the isolated strains,the results showed that the gene combinations of all strains of Streptomyces scab were txt AB+/tom A+/nec1+.The pathogenicity islands of non-pathogenic strains are composed of txt AB-/tom A+/nec1+ and txt AB-/tom A+/nec1-.4.Verifying the pathogenicity of pathogens by radish seedling method,small potato chip method and pot experiment,the results showed that pathogenic bacteria could cause scab lesions on potato tubers,inhibit the growth of radish seedlings,colonize on potato chips and make small potato chips browned.5.Screening the germplasm resources resistant to scab by field experiment,the results showed that the Huashu 5 and Huashu 11 had better resistance to potato common scab among the tested Huashu varieties;the CH524-8 and the M6 had highly resistance to potato common scab among the among the tested resource materials with Solanum chacoense blood.6.The results of pharmaceutical evaluation test indicated that in the experiment in the first half of 2019,the control efficacy of pentachloronitrobenzene on scab was42.73%,and that of zinc thiazole on scab was 31.41%.In the experiment in the second half of 2019,the control efficacy of pentachloronitrobenzene was 57.48%,and that of zinc thiazole was 87.16%.