Streptomycin-Resistant Epiphytic Bacteria with Homologous DNA for Streptomycin Resistance in Michigan Apple Orchards. P. Sobiczewski, Institute of Pomology and Floriculture, 96-100 Skierniewice, Poland. C.-S. Chiou, and A. L. Jones. Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing 48824-1312. Plant Dis. 75:1110-1113. Accepted for publication 6 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1110.

Streptomycin-resistant bacteria were recovered from leaves of apple (Malus domestica) and from leaves and stems of various weed species collected from six orchards in Michigan that had been treated with streptomycin in recent years. Populations of streptomycin-resistant bacteria ranged from 2.0 × 10³ to 5.7 × 10⁵ cfu per apple leaf and from 2.0 × 10⁴ to 1.4 × 10⁶ cfu per gram fresh weight of tissue from weed species. In DNA colony hybridization studies, 97% of 152 strains of streptomycin-resistant gram-negative bacteria contained DNA that hybridized with a 500-bp DNA probe associated with streptomycin resistance in Pseudomonas syringae pv. papulans. These bacteria included strains of P. syringae (several pathovars), P. fluorescens, P. aeruginosa, P. putida, Erwinia amylovora, E. herbicola, Acinetobacter, Aeromonas, Flavobacterium, and a yellow-pigmented Pseudomonas sp. In contrast, DNA from 28 gram-positive bacteria (mostly yellow-pigmented Corynebacterium), three strains of E. herbicola, one strain of P. viridiflava, and one unidentified yellow gram-negative bacterium did not hybridize with the probe. In Southern hybridizations, there was restriction fragment length polymorphism in the SMP3 streptomycin-resistance region among the gram-negative bacteria isolated from apple orchards.