Identification and pathogenicity of phytopathogenic bacteria associated with soft rot disease of girasole tuber in Egypt

Six bacterial isolates were isolated from naturally infected tubers of girasole plants (Helianthus tuberosus L.) cv. Balady showing soft rot collected from experimental Farm of Department of Horticulture, Faculty of Agriculture, in El-Minia University during 2010 and 2011 growing seasons.  Pathogenicity tests showed various virulence for the isolated bacteria toward girasole tubers was found pathogenic and were characterized as rod-shaped, gram negative, α-methyl-d-glucoside medium, reducing substances from sucrose, phosphatase activity and deep cavities on pectate medium. Otherwise, diagnostic tests suggested that the pathogen wasErwinia carotovora sub sp. carotovora. The isolated bacterial caused soft rot of wounded tubers when inoculated into tissues. The bacterial isolates were compared for their degree of pathogenicity as well as for differences in the specific symptoms induced in the different hosts.The tested isolates could infect several host such as fruits of apricot, apple, olive, lemon, squash, eggplant and potato tubers and cloves of bulbs and garlic and onion, root of radish, carrot, sweet potato and rape were infected by the tested isolates. On the other hand, nosymptoms were exhibited on pods of bean and cowpea, faba bean, fruits of pepper and tomato. The extracts of experimentally diseased girasole tubers were active in pectinase at pH 6 and also caboxymethyl cellulose on pH 6 compared to enzyme activities in healthy tissues. Also, the bacterial isolated increased the total and reducing sugars in infected than healthy tissues.   Key words: Girasole, Erwinia carotovora sub sp. carotovora, pectinase and caboxymethyl cellulose, total and reducing sugars.