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Etiology

Identity of Phytophthora Isolated from Milkweed Vine. Eduardo Feichtenberger, Graduate student, Department of Plant Pathology, University of California, Riverside 92521; George A. Zentmyer(2), and John A. Menge(3). (2)(3)Emeritus professor of Plant Pathology, and associate professor of Plant Pathology, respectively, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 74:50-55. Accepted for publication 15 June 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-50.

Comparative morphological, physiological, and pathological tests indicated that isolates of Phytophthora from dying milkweed vine (MWV) (Morrenia odorata) in Florida are P. palmivora, and not P. citrophthora as previously stated. Sporangia of six isolates were caducous with short stalks (2.7 μm). They were ellipsoid to ovoid, and averaged 46 27 μm, with a length/breadth (L/B) ratio of 1.7 and papilla width of 5 μm. Sporangia of isolates of P. citrophthora from citrus were persistent. They were highly variable in shape and size, and averaged 55 35 μm, with an L/B ratio of 1.6 and papilla width of 7 μm. MWV isolates formed oospores in pairings with A1 isolates of P. palmivora and P. parasitica, whereas isolates of P. citrophthora were sterile. Sweet orange plants were resistant to isolates from MWV, but susceptible to isolates of P. citrophthora from citrus. Disc gel electrophoresis of hyphal proteins revealed high percentages of similarity between isolates from MWV and P. palmivora (Morphological Form 1), but not between isolates from MWV and P. citrophthora.