The aim of this study was to characterize Phytophthora isolates from black wattle (Acacia mearnsii) in Southern Brazil, based on phenotypic traits such as morphology, mycelial growth, cultural features, sexual compatibility and pathogenicity, as well as on single strand conformation polymorphism (PCR-SSCP) of rDNA ITS-gene 5.8S region. The isolates presented sporangia with prominent papilla, irregularly sympodial sporangia, heterothalic cultures with amphigynous antheridia, presence of chlamydospore and mycelial growth at temperature above 35°C, allowing the classification of all 12 isolates as P. nicotianae. All isolates were pathogenic to black wattle, causing necrosis on stems without gum formation, with significant differences on aggressiveness (P=0.05). Two populations of P. nicotianae from black wattle can be distinguished based on PCR-SSCP analysis of rDNA; however, this separation has no apparent correlation with phenotypic traits.
gummosis; oomycetes; forest pathology
