Isolation And Identification Of Onion Violet Leaf Spot And Inoculation Method Screening Of Onion At Seedling Stage

Violet leaf spot is one of the important diseases in onion growing period, the disease causes the leaves necrosis in a large area, then the yield and quality declined. But for the pathogenic bacteria of onion violet leaf spot are rarely reported. The study began with the identification of onion violet leaf spot first, biological characteristics of onion violet leaf spot was studied; then the study found a convenient and feasible identification inoculation method of onion at seedling stage. The results were as follows:(1) The onion which showed symptoms of violet leaf spot was used from Heilongjian g province.After the isolation and single spore purification of pathogen, we got H, Q andM these 3 purified strains. Based on the result of pathogenicity observation of pathogen, we confirmed that the H and Q strains were the main pathogenic strains of violet leaf spo t.they were the same fungus. To observe the pathomorphological characteristics and compari son with concerned Alternaria species, then combined with the r DNA ITS sequence analysi s, we confirmed that these two fungus were the same. The pathogens were identified as Alternaria porri(Elliott) Cif.(2)The biological characteristics of pathogen was studied preliminarily under laboratory conditions. The results showed that:for the rate of mycelium growth, the optimum carbon source is maltobiose, the optimum nitrogen sources was NH4 Cl, the suitable temperature range is 26~32℃, the optimum growth temperature was 32℃, the mycelium optimum p H was 7.The mycelium growth speed was the fastest under the alternate condition of light and dark. Asuitable light can promote the pathogen growth of onion violet leaf spot.For the pathogen sporulation: The optimum carbon source was maltobiose, the optimum nitrogen sources was NH4 Cl, the suitable temperature range was 20~26 ℃, the optimum temperature was 24℃, the lethal temperature was 55℃ for the spores,under the continual dark, the number of sporulation was the largest, the number of sporulation was largest was on p H 8, the fungus spores most in alkaline environment.(3)According to the results of orthogonal experiment, the best combination of screening of identification mehods at seedling stage was as follows : acupuncture innoculation method, preserving temperature of 24℃ after innoculation and 5-leaf innoculation seedling stage.