Pseudomonas mediterranea associated with Pseudomonas corrugata on chrysanthemum plants in Sardinia

In this study we have characterized 14 bacterial strains (six Pseudomonas mediterranea and eight Pseudomonas corrugata) isolated from chrysanthemum plants grown in greenhouses located in central-southern Sardinia (insular Italy). Infected chrysanthemum plantlets showed symptoms of rot and blight and, at blooming, chlorosis and necrosis of leaves. In pathogenicity tests all the strains tested induced similar symptoms on chrysanthemum, tomato and pepper plants. Initially, the presence of two different species was ascertained by using different media. Among them, TZCAgar proved to be particularly suitable. The identification and the differentiation of the two species was confirmed by genomic analysis. According to multiplex PCR, performed with specific primers PC1/1, PC1/2 and PC5/1, PC5/2, the six strains of P. mediterranea yilded the typical 600 bp band, while the eight strains of P. corrugate showed the typical 1100 bp band. Cluster analysis of results of rep-PCR performed by using BOXA1R, and ERIC1R and ERIC2 primers, clustered the two species in two distinct groups. On the contrary, Biolog phenotypic fingerprinting analysis identified the 14 strains as P. corrugata. However, P. mediterranea strains could be distinguished from P. corrugata strains on the basis of the metabolic profile determined by Biolog GEN III microplates. P. mediterranea is sensitive to lincomycin antibiotic and oxidize some sugars and organic acids including D- mannose, D-mannitol, L-glutamic acid, L-galactonic acid lactone. To determine their role in the disease, the two bacterial species are currently being tested with experimental inoculations, alone or in combination, onto chrysanthemum, geranium, pepper and tomato plants.