[Gluconobacter spp. and Paenibacillus polymyxa cause spoilage in apparently healthy commercial carrots].

Abstract

Postharvest diseases of carrots are one of the most important concerns in carrot storage, as they affect the shelf life of carrots and cause significant financial losses. In this study, ten commercial carrot samples from supermarkets and local markets in Texcoco, State of Mexico, Mexico, were analyzed for bacterial spoilage after incubation at 28°C in a humidity chamber. Carrots from seven samples developed bacterial spoilage after five days of incubation, of which baby carrots (industrially processed) showed the most severe rot. Twenty-three bacterial strains were isolated from the tissues of spoiled carrots. To identify and characterize the spoilage pathogens, the isolated strains were inoculated into healthy carrots in laboratory tests. Of the 23 strains analyzed, eight caused carrot tissue spoilage. Biochemical and molecular characterization by 16S ribosomal RNA gene sequencing identified Gluconobacter cerinus (1032.2, 1059 and 1070.1), G.kondonii (1027.1), G.wancherniae (1033.1) and Paenibacillus polymyxa (1074.2, 1076 and 1077) as the causal agents of the carrot rot evaluated in this study. In addition, these bacteria showed virulence in other plant pathogenicity tests; Gluconobacter strains induced a hypersensitivity reaction in tobacco leaves and Paenibacillus strains showed pectolytic activity in potato tubers. This study is the first to report G.cerinus, G.kondonii, G.wancherniae and P.polymyxa as causal agents of commercial carrot rot.