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Poster: Diseases of Plants: Disease Detection & Diagnosis


Phytophthora root and crown rot on field-grown lavender plants in 2015
S. JEFFERS (1), S. Sharpe (1), M. Williamson (2) (1) Clemson University, U.S.A.; (2) Clemson University, U.S.A.

Phytophthora nicotianae has a very wide host range, including numerous ornamental plants. In Jun 2015, P. nicotianae was isolated from lavender plants and rooted cuttings (Lavandula angustifolia and L. ×intermedia) with symptoms of Phytophthora root and crown rot (PRCR). The plants recently had been planted in a field in northwestern SC. When this was brought to the attention of the US Lavender Growers Association (USLGA), it was discovered that other growers suspected problems with PRCR—particularly on recently-planted, nursery-grown plants. USLGA members were encouraged to send samples to Clemson University to test for Phytophthora spp. Between Jul and Nov 2015, plant and soil samples were received from 12 states; all plants were cultivars of L. angustifolia or L. ×intermedia. Samples from 11 states were diagnosed with PRCR; Phytophthora spp. were recovered from roots and crowns by isolation on selective media and from soil with a baiting bioassay. Isolates were tentatively identified by morphology, but species identification will be confirmed by DNA sequences. Three species of Phytophthora were isolated: P. nicotianae was isolated most frequently—from samples from 11 states; P. palmivora was found in samples from 3 states; and Phytophthora sp. was found in one sample. Previously, PRCR has been reported on English lavender, L. angustifolia, but not on hybrid lavender, L. ×intermedia. Lavender plants infected with Phytophthora spp. may have come from the nursery. Authors acknowledgeCONICYT PhD fellowship (MV), CONICYT-GO (MV),USM 131562, FONDECYT 1151174& CBDAL grants(MS).