The risk associated with irrigating ornamental nursery plants with water containing Phytophthora.
A. LOYD (1), M. Benson (2), K. Ivors (3). (1) Department of Plant Pathology, North Carolina State University, Raleigh, NC, U.S.A.; (2) North Carolina State University, Raleigh, NC, U.S.A.; (3) North Carolina State University, Mills River, NC, U.S.A.
During the summer of 2011, disease-free plants were irrigated with <i>Phytophthora</i>-contaminated water to determine risk of plant infection. Two nurseries in Western North Carolina were selected because <i>Phytophthora</i> spp. had previously been detected in their irrigation water. Nursery I used water from an on-site retention basin, and nursery II used water from the French Broad River. Containerized <i>Rhododendron</i>, <i>Pieris</i>, and <i>Ilex</i> were used as ‘trap’ plants; water and plant roots were assayed for <i>Phytophthora</i> monthly for a total of 5 mo. Sixty-two isolates were recovered from the two water sources, while only eight isolates were recovered from the roots of plants. Isolates were identified by ITS sequence and included <i>P. cinnamomi</i>, <i>P. heveae</i>, <i>P. hungarica</i>, <i>P. hydropathica</i>, and members of the <i>P. pini-citricola</i> complex, plus six undescribed species. The most frequently recovered species from the river was <i>P</i>. taxon ‘PgChlamydo’, while, <i>P. hydropathica</i> was most frequently recovered in the retention basin. The only species recovered from roots and water was <i>P</i>. taxon ‘PgChlamydo’. Slight root necrosis was observed on <i>Pieris</i> at nursery I, but root rot was not significant on the other plant species at either nursery. Although <i>Phytophthora</i> spp. were present in the irrigation water at about 20 and 75 propagules/liter at nursery I and II, respectively, the risk was low since foliar infection was nil and few root infections developed.<p><p>Keywords: Oomycete, Ornamentals, Woody Ornamentals
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