Research On Occurrence Rule And Control Technology Of BFB In The Process Of Grafted Watermelon Seedling Production

Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli (Aac), was one of the most devastating diseases for watermelon. With the development of intensive seedling technique, grafted seedlings from grafting nursery had become main source of grafted watermelon seedling production. In recent years, BFB had caused significant economic losses in the grafting nursery. This study aimed to find out infection way and propagation rule of BFB in the process of grafted watermelon seedling production and put forward effective control strategy and method of BFB. Moreover, safety production technologys of grafted watermelon seedling were integrated, thus providing theoretical and technical support for the establishing of safety production operating rules of grafted watermelon seedling.1. This study revealed relationship between five factors of in the process of grafted watermelon seedling production and BFB occurrence by artificial inoculation test, namely scion seed, rootstock seed, grafting tool, substrate, grafting method and irrigation way. The result showed that BFB pathogen of contaminated scion seed could infect seedling to cause scion rot death. Contaminated rootstock seed could lead to BFB occurrence of grafted seedlings. Bamboo stick with Aac (concentration≥105cfu/mL) could lead to BFB occurrence of grafted seedling. In the case of continuous grafting50seedling with contaminated bamboo stick (concentration=108cfu/mL), BFB incidence of grafted seedling was97.3%. In the range of107cfu/kg～109cfu/kg, the number of Aac in the substrate was more, occurrence BFB was worse. Resistance of BFB grafted seedlings and self-rooted seedlings both were disease-susceptible types after spraying inoculation. Compared with upper sprinkler irrigation, tidal irrigation could effectively reduce BFB occurrence of grafted seedlings.2. According to the occurrence rule of BFB, this study researched BFB chemical control technology by medicaments screening test and field control effect test, including disinfection technology of scion seed, grafting bamboo stick and substrate. The result showed that seven medicaments could are used to control BFB, namely Kasumin+Bordeaux, Kasumin, stretomycin+oxyteracykine, Kocide3000, Streptomycin Sulfate for Injection,75%alcohol and40%formaldehyde. Soaking seeds contaminated BFB in40%formaldehyde at a dilution of100times for1h before sowing was effective for the control of BFB watermelon seedlings. Moreover, it had no detrimental effects on seeds germination and seedling growth. Soaking the grafting tool of bamboo stick in40% formaldehyde at a dilution of50times or75%alcohol for15min before grafting was effective for the control of BFB. In the case of per kg substrate with109cfu Aac,15days after spraying and mixing with two kinds of medicaments (100kg/m3), the results showed that control efficiency of BFB on the watermelon seedlings for Kasumin+Bordeaux600-fold dilution and Kasumin400-fold dilution were46.4%and30.4%, respectively.3. Hazard analysis of each link on BFB of grafted watermelon seedling production was finished based on the HACCP principle and method. Incorporation with occurrence and control of BFB in the grafting nursery, seven critical control points, control technology and HACCP plan were confirmed in the comprehensive control technology system of grafted seedling BFB. In recent years, grafting nursery suffered huge losses because of BFB occurrence. Application of HACCP in grafting nursery could reduce incidence of BFB, and ensure the quality of production, security and scientific and promote the healthy development of watermelon industry.