Phytophthora nicotianae Breda de Haan (= Phytophthora parasitica Dastur) has a long history as a pathogen of plants. It was first described in 1896, and has a broad host range (Erwin and Ribeiro 1996). In black wattle (Acacia mearnsii De Wild.), it causes a disease called gummosis. It was reported in 1971 in South Africa (Zeiljemaker 1971) and in 2005 in Brazil (Santos et al. (2005). In Brazil, gummosis of black wattle is also caused by P. boehmeriae Sawada (Santos et al., 2006) and P. frigida Maseko, Coutinho & Wingfield (Alves at al., 2016). In South Africa, other agents are P. boehmeriae and P. meadii McRae (Roux and Wingfield, 1997). Gummosis disease is characterized by necrotic bark lesions of varying sizes, with or without exudation of gum. Lesions are located in the collar and in the basal region of the trunk (Santos et al., 2001). In Brazil, evaluation of commercial plantations showed the incidence of gummosis to be over 20% (Santos and Luz, 2007).
Sporangia formed in 10% nonsterile soil extract are papillate, persistent, and predominately ovoid, measuring 56.0 x 35.0 to 33.3 x 24.5 μm (average: 42 x 29 μm) with a length-breadth ratio of 1.4:1. Chlamydospores are terminal or intercalary in the mycelium, with a diameter of 25.4 to 40.3 μm (average of 33.0 μm). P. nicotianae is heterothallic and isolates from both the A1 and A2 compatibility groups are recovered. Oospores measure 23-38 μm in diameter (average: 29 μm). The antheridia are amphygynous (Santos et al., 2005).