Morphological and Molecular Identification of Phytophthora tropicalis as Causal Agent of Crown and Root Rot on Albizia julibrissin
Isolates of a Phytophthora sp. were obtained from soil and root baiting of declining Albizia julibrissin plants grown in soil in an Italian nursery. Identification was performed on the basis of morphological, pathological and molecular features. As main characteristics, isolates did not grow at 35degC, were poorly pathogenic when inoculated on bell pepper plants, and had the average sporangium pedicel length longer than 100, being similar to Phytophthora tropicalis. A comparative study of internal transcribed spacer, beta tubulin, translation elongation factor 1 alpha and cytochrome c oxidase subunit II (CoxII) sequences supported the identification of the isolates as P. tropicalis. Comparison included all the European isolate sequences available in GenBank. Pathogenicity tests reproduced symptoms of root and crown browning and rotting and wilting as originally observed on nursery plants. Considering all the results, we identified P. tropicalis as the causal agent of A. julibrissin decline, crown and root rot. To our knowledge, this is the first report of this host pathogen combination in Italy or elsewhere. P. tropicalis has to be considered a serious threat to agricultural and natural environment because it is highly polyphagous and easy to spread due to its caducous sporangia.