A pith necrosis caused by Xanthomonas perforans on tomato plants

Abstract Pith necrosis is a common disease of tomatoin Europe, mainly caused by Pseudomonas corrugataand other soil-borne species of Pseudomonas. During2011–2012 a survey was conducted in soil-grown tomatocrops in southeastern Sicily (Italy). Plants showedpith necrosis, brown discolouration of the vascular tissues,leaf chlorosis and sometimes wilting of leaves.Thirty bacterial isolates from symptomatic tissues,forming colonies on NA and KB, were identified bymorphological, biochemical and physiological tests.Among them, seven isolates were analyzed for their16S rDNA and 16S–23S spacer region sequence thatresulted in 99 % identity to that of the Xanthomonasperforans type strain (GenBank accession numberGQ46173over 2.085 bp.). Additional sequences of fusA,gapA, gltA, gyrB, lacF, and lepA from one selectedisolate were 100% identical to sequences of theXanthomonas perforans type strain. X. perforans local isolates showed similar genomic patterns with REPPCRand fAFLP, and were clearly distinguishedfrom other Xanthomonas spp. type strains. In steminoculationassays, bacteria isolated from symptomatictomato plants identified as P. fluorescens, P.putida, P. marginalis, P. citronellolis, P. straminea,and Pantoea agglomerans induced discolouration ofvascular tissues, while Pectobacterium carotovorumsubsp. atrosepticum isolates induced soft rot. Conversely,the isolates here identified as Xanthomonasperforans were able to induce pith necrosis, vasculardiscolouration, longitudinal splits and external lesionson stems. This report of X. perforans causing pithnecrosis on tomato represents a potentially seriousproblem that may limit the productivity of tomatocrops.