Phytophthora species were isolated from rivers and streams in eastern Sicily by in situ baiting using floating mesh bag-styrofoam rafts and identified by sequence analysis of internal transcribed spacer (ITS) ribosomal DNA (rDNA). The aim of this study was to investigate the ecological diversity, expressed as Shannon Diversity Index (SDI), of Phytophthora populations from river systems running nine Protected Natural Areas typical of Sicilian riparian plant communities. The major waterways examined included the Alcantara, Anapo and Fiumefreddo rivers on the eastern coast of Sicily, and streams with torrential water regimes such as Sciambro, on mount Etna. The most prevalent species identified in rivers and streams were P. ×cambivora, P. citrophthora, P. frigida, P. gonapodyides, P. hydropathica, P. sp. kelmania, P. lacustris, P. multivora, P. plurivora, P. polonica, P. pseudocryptogea and P. thermophila. High SDI values and a significant proportion of exotic Phytophthora species were found in 50% of the examined river systems, particularly in systems highly disturbed by human activities (e.g. the Fiumefreddo river, a small watercourse in a small natural reserve recently established in a highly anthropized area). By contrast, the naturalized systems showed the lowest diversity (e.g. the Sciambro stream, a seasonal water course at high altitude in the Mount Etna regional park, crossing a single-tree-species forest of black pine).
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