Six bacterial isolates were isolated from naturally infected tubers of girasole plants (Helianthus tuberosus L. cv. Balady) showing soft rot, which were collected from the experimental farm of the Faculty of Agriculture, Department of Horticulture, El-Minia University, during 2010 and 2011 growing seasons. Pathogenicity tests showed the virulence of the isolated bacteria in girasole tubers which harbored the pathogen; the bacteria 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 ssp. carotovora. The isolated bacteria 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 range such as fruits of apricot, apple, olive, lemon, squash, eggplant, potato tubers, cloves of bulbs, garlic and onion; root of radish, carrot, sweet potato and rape, were infected by the tested isolates. On the other hand, no symptoms 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. The bacterial isolates also increased the total and reducing sugars in infected than healthy tissues.
Key words: Girasole, Erwinia carotovora ssp. carotovora, pectinase andcaboxymethyl cellulose, total and reducing sugars.
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