First report of bacterial soft rot on onion caused by Dickeya sp. (ex Pectobacterium chrysanthemi ) in Spain

In summer 2005, following heavy storms, soft rot symptoms were observed at the base of central leaves of onion plants ( Allium cepa ) in fields with drip irrigation in Zaragoza, northeastern Spain. The incidence of disease was approx. 10%. Longitudinal sections revealed that lesions developed downward, so that the inner layers of bulbs also appeared macerated. Isolations from diseased leaves and bulbs yielded pectolytic bacteria on crystal violet pectate (CVP) medium and colonies were characterized after purification on King’s B medium. Isolates were Gramnegative rods, oxidase negative, facultatively anaerobic, degraded pectate and rotted potato slices. They grew at 37 ° C, were sensitive to erythromycin, positive for phosphatase, indole production and malonate utilization, while negative for acid production from trehalose and α -methyl glucoside. The bacteria were further identified by ELISA, PCR amplification (Nassar et al ., 1996) and biovar discrimination tests (Ngwira & Samson, 1990) as biovar 3 of the species Pectobacterium chrysanthemi. Suspensions (10 8