Nine Phytophthora spp. isolates from the rhizosphere of infected orange (Citrus sinensis) plants in Alagoas were characterized based on colony morphology, morphology and morphometry as well as reproductive structures, and cardinal growth temperatures. All cultures were heterothallic, with papillate, ovoid or subspherical sporangia measuring 24.6 - 78.7 µm long x 16.4 - 49.2 µm wide, average 49.1 x 33.3 µm. The length-breadth ratio was 1.1 - 2.3, average 1.5. Chlamydospores were mostly terminal, 13.1 - 45.9 µm in diameter, average 27.3 µm. Oogonia were globose, 14.8 - 34.4 µm in diameter, average 26.4 µm containing aplerotic oospores 11.5 - 29.5 µm in diameter, average 22.7 µm and amphigynous antheridia 6.6 - 16.7 µm x 8.2 - 16.7 µm (average 10.6 µm x 12.0 µm). The greatest mycelial growth was observed at 25-30 ºC in modified carrot agar medium. All isolates grew at 35 ºC and were pathogenic to lemon (Citrus limonia) cv. Cravo seedlings and ripened fruits of orange (C. sinensis) cv. Pera. The isolates were identified as Phytophthora nicotianae (= P. parasitica) of the A1 mating type.
