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Understanding the impact of Pythium species on floricultural crops in North Carolina.
E. LOOKABAUGH (1), K. Ivors (1), M. Benson (1), B. Shew (1). (1) North Carolina State University, Raleigh, NC, U.S.A.

Although <i>Pythium</i> is frequently diagnosed in floricultural crops, the practical significance of these findings often is unclear. Floricultural crops in NC have not been systematically sampled for the presence of <i>Pythium</i>, the predominant species have not been identified, and the extent of mefenoxam resistance is unknown. Herbaceous ornamentals exhibiting symptoms of Pythium root rot were collected from 18 greenhouses in 14 counties in NC. Roots were assayed on selective media for the presence of <i>Pythium</i>. Isolates were recovered from 24 host species. Isolates were screened for mefenoxam sensitivity on 5% clarified V8 agar amended with 100 ppm mefenoxam, dispensed in 48-well micro-titer plates. Colonization by 3 samples/isolate was scored after 24 to 48 h on a scale of 0 (no growth) to 5 (entire well colonized). Of 277 isolates, 54.2% were considered resistant to mefenoxam (mean score > 4). Selected isolates were identified by sequencing of the ITS rDNA region. Twelve species were identified, with <i>P. myriotylum</i>, <i>P. aphanidermatum</i>, and <i>P. irregulare</i> comprising 85% of the 94 isolates sequenced thus far. <i>P. aphanidermatum</i> was recovered at 8 locations, <i>P. myriotylum</i> at 5, and <i>P. irregulare</i> at 7. Eight locations had >1 species present. All isolates (19) of <i>P. myriotylum</i> were sensitive to mefenoxam. We found both sensitive and resistant isolates of <i>P. aphanidermatum</i> and <i>P. irregulare</i>. Resistant and sensitive strains of the same species were found within the same greenhouse. <p><p>Keywords: Oomycete, Ornamentals, Herbaceous Ornamentals

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