Caracterização morfológica, molecular e patogênica de espécies de Phytophthora associadas aos citros

Abstract

Phytophthora root rot is one of the most important diseases of citrus in Brazil and other countries. The causal agents are species of Phytophthora, being the most important P. nicotianae, the prevalent and widely distributed species, and P. citrophthora, less frequent in tropical regions. As the first step to develop a PCR based detection method of the disease, the variability of a population of P. nicotianae from citrus and other host was evaluated by morphological characters, phylogeny and pathogenicity tests. Isolates of P. nicotianae were identified from citrus, tobacco, black acacia and Kalanchoe, showing characteristics such as predominantly spherical to, terminal or intercalary, persistent and papillate, with numerous chlamydospores, and amphigynous antheridia. Isolates from citrus, identified as P. citrophthora showed oval or variable, papillate sporangia, frequently bipapillate and persistent, without chlamydospores and oogonium. All isolates of P. nicotianae were pathogenic to citrus and tobacco seedlings, as well as to citrus fruits. P. citrophthora was pathogenic only to seedling and fruits of citrus. Phytophthora capsici did not show pathogenicity to citrus nor tobacco. In the phylogenetic analysis all isolates of P. nicotianae grouped together in a unique clade, together with sequences recovered from Genbank, with 100% bootstrap support. These results indicate low infra-specific variability in this species and lack of specificity towards host plants. This information will be useful to develop a rapid PCR detection method for these citrus pathogens.