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Organically Managed Soils Reduce Internal Colonization of Tomato Plants by Salmonella enterica Serovar Typhimurium

April 2013 , Volume 103 , Number  4
Pages  381 - 388

Ganyu Gu, Juan M. Cevallos-Cevallos, Gary E. Vallad, and Ariena H. C. van Bruggen

First, second, and fourth authors: Emerging Pathogens Institute and Department of Plant Pathology, University of Florida, Gainesville 32611; and third author: Gulf Coast Research and Education Center, University of Florida, Wimauma 33598.

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Accepted for publication 28 December 2012.

A two-phase experiment was conducted twice to investigate the effects of soil management on movement of Salmonella enterica Typhimurium in tomato plants. In the first phase, individual leaflets of 84 tomato plants grown in conventional or organic soils were dip inoculated two to four times before fruiting with either of two Salmonella Typhimurium strains (109 CFU/ml; 0.025% [vol/vol] Silwet L-77). Inoculated and adjacent leaflets were tested for Salmonella spp. densities for 30 days after each inoculation. Endophytic bacterial communities were characterized by polymerase chain reaction denaturing gradient gel electrophoresis before and after inoculation. Fruit and seed were examined for Salmonella spp. incidence. In phase 2, extracted seed were planted in conventional soil, and contamination of leaves and fruit of the second generation was checked. More Salmonella spp. survived in inoculated leaves on plants grown in conventional than in organic soil. The soil management effect on Salmonella spp. survival was confirmed for tomato plants grown in two additional pairs of soils. Endophytic bacterial diversities of tomato plants grown in conventional soils were significantly lower than those in organic soils. All contaminated fruit (1%) were from tomato plants grown in conventional soil. Approximately 5% of the seed from infested fruit were internally contaminated. No Salmonella sp. was detected in plants grown from contaminated seed.

Additional keywords: endophytic bacterial community, seed contamination.

© 2013 The American Phytopathological Society