Caracterização fenotípica e genotípica de isolados de Pseudomonas spp. do tomateiro tutorado no Brasil

Abstract

The bacterial incidence caused by the bacteria genus Pseudomonas cause considerable losses in tomato yield. This genus has population the isolates with great genetic diversity, it can directly influence the pathogen aggressiveness level. The objective of this work was to characterize 43 isolates of Pseudomonas spp. obtained from samples of tomato stems or leaves with symptoms of pith necrosis or leaf lesions, respectively, regarding phenotypic and genotypic aspects. Bacterial isolates were morphological and biochemically characterized by Gram tests, anaerobic growth, King B medium and LOPAT tests. Molecular analysis was performed by rep-PCR (REP, ERIC and BOX primers), specific primers and genetic sequencing of the 16S region of from isolates part. To evaluate aggressiveness, two assays were conducted, one using the isolates from the stem and the another from the tomato leaf. In both experiments healthy tomato plants cv. Santa Clara VF5600 were inoculated with bacterial suspension at a concentration 1.0 x 108 CFU mL-1, and the severity of the disease was evaluated and the Area Under The Disease Progression Curve calculated. Morfologically, all colonies were circular and bright, most then of transparent and with smooth edges. The elevation varied between straight, slightly elevated and convex, and the coloration in shades of straw color. Biochemically, the isolates were classified into groups II, IVb, Va and Vb the LOPAT tests, one isolate as P. corrugata and two biochemically undetermined isolates. Molecularly the isolates shoued high genetic diversity by rep-PCR, and it was not possible to relate the molecular characteristics with the place of origin. With the specific primers only the UFU B39 isolate was identified as P. corrugata. Genetic sequencing confirmed the identified of several isolates such as P. putida and P. fluorescens, and also P. syringae pv. tomato that presented biochemical variation. In the aggressiveness tests in the stem, the isolates UFU B39 and UFU H24 were the most aggressive, and in the leaf test there was no difference in the isolates aggressiveness. It was concluded that the isolates showed low morfological variation, high biochemical and molecular variation and different levels of stem aggressiveness. This is the first report of P. putida and P. fluorescens causing disease in staked tomato plants in Brazil.