Epiphytic and endophytic microorganisms associated to different cultivar of tomato fruits in greenhouse environment and characterization of beneficial bacterial strains for the control of post-harvest tomato pathogens

Abstract

Several bacterial and fungal diseases affect greenhouse-grown tomato crops, causing severe annual yield losses worldwide. The need to reduce chemical compound applications has encouraged the search of alternative approach for the control of tomato diseases, including the use of biological control agents. The presence of total and beneficial microbial populations was investigated on the surface and in the pulp of seven cultivars of tomato fruit coming from eleven greenhouses in the Pachino district (south-east of Sicily), recognized by the European Community with the "Protected Geographical Indication" label. Principal component analysis (PCA) showed that epiphytic and endophytic microbial populations clustered into groups according to the areas of origin. Approximately 240 tomato fruit-associated bacterial isolates were selected and a high percentage of them showed antagonistic activity against Clavibacter michiganensis subsp. michiganensis, Pseudomonas syringae pv. tomato, Xanthomonas euvesicatoria pv. perforans, Botrytis cinerea and Alternaria alternata. Analysis of the 16S rRNA gene sequences revealed a predominance of bacteria in Bacillus and Pseudomonas genera, followed by Citrobacter and Enterobacter. The presence of these genera differed according to the geographical areas of tomato samples, whereas their antagonistic capabilities varied according to the five tomato pathogens. The in vitro effectiveness of eight representative bacterial strains belonging to Pseudomonas, Bacillus and Enterobacter genera was confirmed in in vivo assays, carried out on tomato fruit artificially inoculated with A. alternata and B. cinerea. Altogether, these results revealed differences in population density of native microbiota of "Pomodoro di Pachino" fruits and allowed the selection of antagonistic bacterial strains that can be applied in field and in postharvest conditions as alternatives to chemical compounds.

Keywords: 16S rRNA gene; Antagonistic bacteria; Carposphere microbial communities; PGI tomatoes; Postharvest fungal pathogens; Principal component analysis (PCA).