Distribution and host specificity of Phytophthora species found in Indiana nurseries, greenhouses, and landscape plantings
Abstract
From 2006 to 2008, samples with Phytophthora blight and crown rot symptoms were collected as part of the USDA-APHIS Phytophthora ramorum nursery survey and submitted by additional outside sources to the Purdue Plant and Pest Diagnostic Laboratory. From 30 sites, 121 Phytophthora isolates were obtained from 1657 host samples consisting of 32 host genera. Comparison of the internal transcribed spacer (ITS) regions of the ribosomal DNA identified 13 Phytophthora spp. A majority of the isolates was either P. citricola (35.9 %) or P. citrophthora (27.4%). The remaining isolates consisted of P. cactorum, P. cactorum x hedraiandra, P. cambivora, P. capsici, P. dreschleri, P. hedraiandra, P. nicotianae, P. nicotianae x cactorum, P. palmivora and P. syringae. Four isolates were confirmed to be hybrids of P. cactorum x hedraiandra by cloning and sequencing the ITS region. Three P. cactorum x hedraiandra isolates came from Rhododendron plants from the same site. One other P. cactorum x hedraiandra hybrid isolate was recovered from Dicentra from a site separate from the other hybrids. Dicentra is not a reported host of either of the parental species, P. cactorum or P. hedraiandra. Koch’s postulates of the hybrid Phytophthora were fulfilled on Dicentra and demonstrated an increased host range because of hybridization.
Degree
M.S.
Advisors
Beckerman, Purdue University.
Subject Area
Plant Pathology
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