Isolation of Phytophthora palmivora pathogenic to citrus in Florida.

A Phytophthora sp. recovered from soil in a citrus orchard near Fort Pierce, Florida, was characterized and designated as P. palmivora. It produced papillate, caducous sporangia (50 × 27 μm) with a pedicel 3 μm long. All isolates were A 1 and mated readily with A 2 mating types of P. palmivora from cacao and P. parasitica from citrus. Oogonia, oospores, and chlamydospores averaged 30, 25, and 34 μm, respectively, in diameter. The optimum temperature for growth was 30 C, with little or no growth at 15 or 33 C. The citrus isolate of P. palmivora was as pathogenic as or more so than P. parasitica to fibrous roots of sweet orange, sour orange, and Swingle citrumelo (.)