Occurrence of Pseudomonas mediterranea on tomato in Brazil

During the years 2005-2008, symptoms of tomato pith necrosis (TPN) were observed that caused significant losses in several commercial cropsin the State of São Paulo, Brazil. Symptoms were similar to those reported for Pseudomonas corrugata or P. mediteranea and often first appeared near wounds where side-shoots had been removed, causing external dark brown necrosis of stems and degradation of pith (Fig. 1). Isolations from diseased plants on King’s medium B resulted in the growth of a bacterium with smooth or wrinkled colonies producing a greenish-yellow, non-fluorescent, diffusible pigment. Isolates were tested for pathogenicity on young tomato plants by placing a drop of bacterial suspension (10⁸cfu/ ml) in the leaf axils and then pricking the stem with a sterile needle. Control plants were similarly treated using sterile distilled water. Plants were maintained in a glasshouse with temperatures ranging from 25 to 30º C. The type strains of Pseudomonas corrugata (IBSBF 647^T) and P. mediterranea (IBSBF 2059^T) were used for comparative purposes.

The pathogenicity of isolateswas confirmed two weeks after inoculation (Fig. 2). The bacteria were aerobic, positive for oxidase, arginine dihydrolase, nitrate reduction to nitrites, meso-tartrate and histamine utilization, and negative for levan production and aesculin hydrolysis. In rep-PCR using BOX primers, the isolates showed identical profiles to those of the type strain of P. mediterranea (Fig. 3). In PCR using the primers type I ( PC5/1 and PC5/2) for P. corrugata and type II (PC1/1 and PC1/2) for P. mediterranea (Catara et al., 2002) the identities of strains were confirmed by the amplification of a 600 bp DNA fragment specific to P. mediterranea (Fig. 4). Until now, only P. corrugata had been reported as causing TPN in Brazil (Martins et al., 1990; Rodrigues-Neto et al., 1990). Consequently, this is the first report of P. mediterranea causing TPN in Brazil.