PHENOTYPIC AND GENETIC CHARACTERIZATION OF ERWINIA CAROTOVORA SUBSP. CAROTOVORA STRAINS ISOLATED FROM GRAFTED TOMATO IN SARDINIA.

Recently a disease symptomatically similar to that induced by Erwinia carotovora in tomato (Lycopersicon aesculentum Mill) has been observed in some Sardinian greenhouses on cvs Cuore di Bue and Cencara grafted onto Beaufort, He-Man, Camone, and Cencara. Symptoms, which developed during ripening of the first fruit, consisted of 10 to 15 cm long dark brown/black longitudinal lesions of the stem, soft stem rot and dissolution of the pith, vascular tissue discoloration, wilting and collapsing of the whole plant. About 8% of the plants were infected in the damper greenhouse areas. Numerous bacterial colonies were obtained on YS from diseased internal stem tissues. Seven colonies were selected based on their ability to induce rotting of potato slices and a hypersensitive response in White burley tobacco leaves. For pathogenicity tests, a drop of bacterial suspension was placed on the primary leaf node of the stem of five four-week-old greenhouse tomato plants. Five isolates could infect artichoke, basil, bean, fennel, zucchini, melon, pepper, grafted and non-grafted tomato, and white cabbage. One isolate could not infect white cabbage and one basil, zucchini, and white cabbage. Pathogenicity tests and morphological, biochemical and physiological characterisation showed that the seven bacterial isolates belonged to Erwinia carotovora subsp. carotovora. Identification was confirmed by ELISA using the serum anti E. carotovora subsp. carotovora CFBP 2046. Preliminary identification was also made by PCR using Y1 and Y2 primers. Restriction fragment length polymorphism (RFLP) analysis of the 434 bp PCR amplification product placed two of the seven isolates in RFLP group 8, but five isolates did not fit in any of the known RFLP groups. This seems to be the first record of this disease on greenhouse tomatoes in Italy.