Identification Of Two Kinds Of Bacterial Diseases On Cucumis And Bactericide Screening Indoor

Through the observation and investigation of seeding reproduced in Southern China base at Sanya,Hainan province,it is found that cucumber bacterial disease occurred seriously,and the incidence was 99%.This is the first and systematically reported about the symptoms and pathogens of two cucumber bacterial diseases in Southern China base at Sanya,Hainan province.The host range,bactericide screening and disease resistance of the two strains of bacteria were measured.Cucumber bacterial soft rot pathogen(SY-9)infestes the leaves,the edges of leaves appeared yellow spots,the lesions gradually enlarge,turn brown,and became wet rot,spread to the center of the leaves gradually.Cucumber bacterial leaf spot pathogen(SY-21)mainly infects cucumber leaves,the symptoms on leaves are blade thin,light green,yellow halo around the lesion,the lesions are irregular and the center become brown.Severely affected portions of leaves were chlorotic,and lesions coalesced to produce broad necrotic areas.Diseases develop rapidly under appropriate temperature and humidity conditions,resulting in total loss of yield finally.Two bacterial strains pathogenic measured,and then were cultivate character,gram stain,KOH rapid detection,physiological and biochemical characteristics measured,16S rDNA sequence analysis,housekeeping genes sequence analysis,phylogenetic tree to determine its classification home culture.The two strains SY-9 and SY-21 result of gram stain were red,propagation of non-stick wire in 3%KOH solution,both of them were identified as gram-negative bacteria(G’).SY-9 didn’t produce blue pigment on the PDA,can grow at 37℃ and 5%sodium chloride,can produce acid from lactose,trehalose,melibiose,cellobiose,it is possible to utilize galacturonic acid salts,pectate can be degraded,the potato can be softened and also can produce 3-hydroxybutanone.16S rDNA and housekeeping genes rpoB sequence analysis showed that:strain with the highest sequence similarity is Pectobacterium carotovorum subsp.carotovorum,homology of 99%or more.According to the phylogenetic tree situation,combined with the results of morphological identification,physiological and biochemical test results,the strain SY-9 identified as[Pectobacterium carotovorum subsp.Carotovorum(Jones)Bergey.].SY-21 was catalase positive,oxidase positive,can fluorescent blue(under UV light)on King’s,can grow at 30 ℃,but can’t grow at 41℃.It is possible to utilize glucose,β-alanine and fructose as carbon sources.Can’t hydrolyze Tween 80 and liquefy gelatin.16S rDNA and housekeeping genes rpoB sequence analysis showed that:strain with the highest sequence similarity is Pseudomonas cichorii,homology of 98%or more.According to the phylogenetic tree situation,combined with the results of morphological identification,physiological and biochemical test results,the strain SY-21 identified as[Pseudomonas cichorii(Swingle)Stapp.].The host range was determined for each of the two pathogens.Through injection method identified 22 plants that can be infected by Pectobacterium carotovorum subsp.carotovorum,no injury spray method can infect 11 kinds of plants,clear the host range of the pathogen.Through injection method identified 18 plants that can be infected by Pseudomonas cichorii,no injury spray method can infect 12 kinds of plants,for the first time clear the host range of the pathogen.Inhibition zone method,the indoor toxicity of 13 kinds of bactericides on two strains were studied,the results showed that:12%Zhongshengmycin WP agent best control effect in Pectobacterium carotovorum subsp.carotovorum,,the inhibition ratio was 78.67%,the linear regression equation was Y=3.0425x+3.9131,EC50 was 0.0733mg/mL.72%streptomycin WP agent best control effect in Pseudomonas cichorii,the inhibition ratio was 60%,the linear regression equation was Y=0.9629x+1.1099,EC50was 3.6283mg/mL.Injection method,the resistance tests of 20 different cucumber varieties were performed.The results showed that Tangshan Qiugua No.l,Xinjinchun No.4 and Chaoba 808 had better resistance to bacterial soft rot of cucumber.Unbeaten fruit cucumber,Zhongnong No.8 and spring-to-autumn cucumber had better resistance to bacterial leaf spot of cucumber.Pathogenicity can be used to guide field production.