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Comparing populations of epiphytic bacteria in Pennsylvania’s organic and conventional stone fruit orchards as it relates to bacterial spot management
S. BARDSLEY (1), M. d. Jimenez-Gasco (1). (1) Penn State Univ, University Park, PA, U.S.A.

Bacterial spot of stone fruit (caused by <i>Xanthomonas arboricola</i> pv. <i>pruni</i>) remains the most important bacterial disease of peach and nectarine in the eastern US and has greatly hindered the establishment of organic stone fruit orchards in this region. Despite that, no bacterial spot was found in two organic peach orchards in Adams County, PA. The objectives of this research were to monitor and identify populations of bacterial epiphytes in organic and conventional stone fruit orchards, including bacterial epiphytes resistant to the antibiotic oxytetracycline, the primary antibiotic used in conventional management. Samples were taken from 6 conventional and 2 organic stone fruit orchards. Bacteria growing on media amended with 10 and 25 mg/L oxytetracycline were recovered from all orchards. Comparisons made between the overall bacterial populations obtained from organic and conventional orchards, based on morphological characteristics, demonstrated that bacterial populations from organic and conventional orchards were completely different. Gram positive bacterial colonies and yeasts predominated populations recovered from the two organic orchards while the majority of bacterial colonies recovered from the conventional orchards were Gram negative.

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