Identity ofPhytophthoraIsolated from Milkweed Vine

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Abstract
Comparative morphological, physiological and pathological tests indicated that isolates of Phytophthora from dying milkweed vine (MWV) (M. odorata) in Florida [USA] are P. palmivora and not P. citrophthora as previously stated. Sporangia of 6 isolates were caducous with short stalks (2.7 .mu.m). They were ellipsoid to ovoid, and averaged 46 .times. 27 .mu.m, with a length breadth (L/B) ratio of 1.7 and papilla width of 5 .mu.m. Sporangia of isolates of P. citrophthora from citrus were persistent. They were highly variable in shape and size, and averaged 55 .times. 35 .mu.m, with an L/B ratio of 1.6 and papilla width of 7 .mu.m. 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.