Archivio Journal of Plant Pathology

Abstract:

Cymbidium grandiflorum cv. Vanguard with symptoms of soft rot was observed in spring 2013 in Hangzhou, China. Rotting was initially confined to several small water-soaked lesions, which enlarged rapidly in diameter. The affected areas became soft and mush while its surface turned discolored and somewhat depressed. The severely infected plants gave off repulsive odor and died. Five bacterial strains coded CH-1 to CH-5(CEC2013-2) isolated from the infected plants showed characteristics similar to those of the standard reference strains of Pectobacterium carotovorum subsp. carotovorum LMG2404 and P. carotovorum subsp. carotovorum SD-6 in phenotypic tests, including results of Biolog (version 5.2), pathogenicity tests, and FAME, using the Microbial Identification System with aerobic bacterial library (TSBA 6.0). Bacterial isolates were facultative aerobic, rod-shaped, gram-negative, peritrichous flagella, and did not produce green-fluorescent diffusible pigment in King’s Medium B. Colonies on nutrient agar were grey white, slightly raised with smooth margins. Hypersensitive reaction was observed in tobacco. All isolates were identified as P. carotovorum subsp. carotovorum with Biolog similarity of 0.651–0.756 and FAMEs similarity of 0.538-0.703. Crystal violet pectate (CVP) medium test of the strains showed characteristic of P. carotovorum. Identification was confirmed by the specific PCR primers of P. carotovorum subsp. carotovorum pmr A F0145 and E2477 (Mohamed et al., 2014). Inoculation of healthy C. grandiflorum cv. Vanguard plants reproduced the symptoms observed in natural infections, which differ from the bacterial stem rot of poinsettia induced by Pectobacterium chrysanthemi (Rungnapha et al., 2008). The bacterium was re-isolated from symptomatic plants of C. grandiflorium. To the best of our knowledge this is the first report of soft rot of C. grandiflorum caused by this bacterium in China.