Isolation And Identification Of The Causal Pathogens For Summer Canker On Kiwifruit And Screening Of Biocontrol Strains

Kiwi is a fruit with high nutritional value.With the expansion of artificial planting area of kiwifruit,more and more pests and diseases on kiwifruit.In recent years,a bacterial disease of kiwi fruit summer canker has been discovered and reported in South Korea,Zhejiang,Jiangxi,Sichuan in China.At present,there is no relevant report on the prevention and control of this disease,but chemical prevention and control methods are mainly used for other diseases,and chemical prevention and control have many disadvantages such as polluting the environment,affecting food safety,and making plants resistant to diseases.On the contrary,biological control has many advantages such as being environmentally friendly and free of pesticide residues.Therefore,biological control methods have good development prospects for the control of plant diseases and insect pests.In the kiwi fruit orchard in Chetianwan Village,Zhongfeng Town,Ziyuan County,Guilin City,Guangxi Zhuang Autonomous Region,the dominant strain were isolated from the susceptible kiwi fruit tissues,named GX1.The strain was round,milky white,smooth,slightly convex and other features.After pathogenicity tests,it was found that the strain can cause hypersensitive response in tobacco,brown necrosis on kiwifruit leaves and live leaves,and xylem browning on detached branches and live branches.Physiological and biochemical identification of GX1 found that the strain can use lactose,arabinose,cellobiose,melibiose and sorbitol,can liquefy gelatin and soften potatoes,but cannot use sodium malonate,and cannot It can’t grow under 5% Na Cl even at 37°C.It is positive for contact enzymes,and negative for phenylalanine dehydrogenase,oxidase,gram stain,and starch hydrolysis.After Biolog identification,GX1’s utilization of carbon sources and other chemical substances is similar to the characteristics of Pectobacillus carotovora strains.Through 16 S r DNA sequence sequencing and establishment of phylogenetic tree analysis,it was found that the GX1 strain had the highest homology with Pectobacterium carotovorum subsp.actinidiae with the accession number NR125539.1.PCR amplification was performed with specific primers Pca F1/R2,and a 343 bp band of interest was obtained after agarose electrophoresis,which proved that the strain was indeed Pectobacterium carotovorum subsp.actinidiae.The growth curve of this strain was determined,and it was found that when the fermentation time was 12 h,this strain had the largest amount of bacteria.In summary,the GX1 strain is Pectobacterium carotovorum subsp.actinidiae.Samples were collected from the kiwifruit orchards in Zhongfeng Village and Chetianwan Village,and strains were isolated from the endogenous and exogenous kiwifruit.A total of 483 strains were obtained.Among them,the number of strains isolated from the samples of Chetianwan village orchard is more than the number of strains isolated from the orchard of Zhongfeng village,and the number of strains isolated from the rhizosphere part of the two places is the largest,accounting for 33.58% of the total number of strains.A plate antagonism test was carried out on the isolated strains,and it was found that 14 strains had obvious inhibition zones.Among them,the inhibition zone of 3 within 1-4 roots and 1 within2-8 branches were larger,both above 10 mm..Through the biological control test of in vitro branches,it was found that the control effect of 1-4 root 3 was the highest,reaching 60.47%,and the strain 1-7 leaf 1 also had a good control effect.In the pot experiment,these two strains also showed good control effects.Therefore,these two strains with relatively stable control effect are the first choice for subsequent field trials and production of biological pesticides.The 16 S r DNA sequence analysis of these strains showed that except for the 1-4 roots 3 were Paenibacillus sp.,the rest belonged to Bacillus sp..This study mainly isolates and identifies pathogens in Guangxi kiwifruit orchards,and screens out effective biocontrol strains.This lays the foundation for subsequent field trials and also provides methods for the prevention and control of local kiwifruit summer canker,and hopes to reduce the economic loss caused by disease.