Isolation And Identification Of Pathogens Of Potato Scab And Screening Of Biological Fungicides For Control In Ningxia

Potato scab was one of the important potato diseases in Ningxia and even the whole country.It occurs in various regions of china every year,which seriously affects the quality and yield of potatoes.It was of great significance for the sustainable development of potato industry to clarify the symptoms,occurrence regularity,pathogen species and control measures of potato scab in Ningxia.In this study,in October 2020 and November 2021,in the early stage of potato harvesting,a random survey on the occurrence of potato diseases was conducted in different agricultural ecological types in Ningxia,involving 4 prefecture-level cities,9 counties,and 17 townships in Ningxia.At the same time,the isolation and identification of pathogenic bacteria were carried out,and the biological control technology of potato scab was explored by the combination of pot experiment and field experiment.The main research results are as follows:1.The incidence and distribution area of potato scab in Ningxia were found out,the incidence period and the harmful parts of potato scab were determined,and the main factors affecting the incidence of potato scab were analyzed.And the main factors were variety,farming method,soil type and irrigation method.The incidence of potato scabby disease was found in 11 of the 17 survey sites in Ningxia,accounting for 64.7%of the total number of survey samples,mainly distributed in Pingluo,Haiyuan,Xiji,Yuanzhou and Tongxin counties(towns),and 6 sites,accounting for 35.3%of the total number of survey samples,were not found,mainly distributed in Wanglejing township of Yanchi county,Fengji Ditch township and Qingshan township,Gaozhuang township of Tongxin county,Haoshui township of Longde county and Fengzhuang township of Pengyang county.More than 15%of the cases were mainly distributed in Caowa Township of Haiyuan County,Jiangtai Township and Malian Township of Xiji County.The onset period of potato scab was in the tuber formation stage and the onset site was in the tuber.The number of diseased samples on Qingshu9 was higher,and the number of samples without disease on Xisen6 was relatively high.The incidence of scab disease was more common in the continuous cropping method,and no scab disease occurred in the potato scab planted in the rotation planting method.The number of investigations was relatively higher,and the number of investigations without the incidence of potato scab planted on new soil was higher.The incidence of drip irrigation was higher,and the incidence of dry land without irrigation was lower.2.The symptoms and distribution areas of Ningxia potato scab disease spots were clarified,strains with actinomycete characteristics were isolated,and pathogenic strains were obtained,and the pathogenicity of the diseased strains was clarified.There are 5 species of scab bacteria.There were three types of potato scab spots in Ningxia,which were flat,raised and sunken.The flat type was distributed in Shizuishan city.The concave type is distributed in Wuzhong City.Both flat and sunken types appeared in Zhongwei city and Guyuan city has all three.Sixty-nine strains with actinomycetes were isolated from potato scab,among which 17 were the dominant strains,11 in Guyuan city and 4 in Wuzhong City,respectively.Eight pathogenic strains were obtained after pot grafting verification,including strains X-1,X-2、g4、g1-2、g3、GX-1、GX-3 and GX-5.The small potato chip method was used to identify the differences among strains,among which strains X-1,X-2 and g4 had the largest area of disease spots.Through 16S rDNA sequence analysis,it was clarified that there were 5 species of potato scab pathogens in Ningxia,which were S.europaeiscabiei,S.deccanensis,S.anulatus,S.globisporus and S.galilaeus.S.anulatus,S.deccanensis and S.globisporus were identified as highly pathogenic strains by small potato chip method,all of which came from Malian Township of Xiji County,which had a high incidence of scab.3.The plate confrontation experiment confirmed that Trichoderma harzianum M-17 biological agent has different inhibitory ability to different pathogens.Through pot experiment and field experiment,the investigation of potato seedling emergence rate,control effect and rhizosphere soil microorganism quantity screened out the suitable biological bacteria agent to control potato scab.The results of scanning electron microscopy showed that Trichoderma harzianum M-17 had strong inhibition ability against pathogen X-2.The results of pot experiment and field experiment showed that potato seedling emergence rate and control effect were the highest under the treatment of Trichoderma harzianum+Zhongshengmycin,reaching 86.27%,66.19%(pot experiment),82.38%,63.29%(field experiment).The disease index of Trichoderma harzianum was 5.92(pot experiment)and 6.85(field experiment)under Trichoderma harzianum M-17+Zhongshengmycin.According to the statistical analysis of beneficial microorganisms in soil rhizosphere,the treatment of Trichoderma harzianum M-17+Zhongshengmycin can increase the number of beneficial microorganisms in soil and reduce the occurrence of diseases.In conclusion,Trichoderma harzianum M-17+Zhongshengmycin treatment has the best effect on improving potato yield and commercial potato yield.