|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