First Report of Phytophthora Blossom Blight of Chrysanthemum Caused by Phytophthora nicotianae

In October 2000, chrysanthemums (Dendranthema × grandiflorum) cv. Debonair exhibiting blossom blight were submitted to the Plant Diagnostic Lab at Auburn University by a commercial greenhouse where most of the potted plants of this cultivar were symptomatic. At a local retail outlet, approximately 95% of the plants of the same cultivar of chrysanthemum had a similar blossom blight. Blighted petals were examined microscopically, and nonpapillate, internally proliferating sporangia (40 to 45 μm in length), characteristic of some species of Phytophthora, were observed. A species of Phytophthora was isolated repeatedly on PARP selective medium (corn meal agar containing pimaricin, ampicillin, rifamycin, and pentachloronitrobenzene). Isolates recovered were grown on V8 juice agar, under fluorescent lights and in darkness, at room temperature. These isolates were identified as Phytophthora nicotianae (= Phytophthora parasitica), on the basis of morphological and cultural characteristics. Sporangia were papillat...