Phytophthora pseudocryptogea , P. nicotianae and P. multivora Associated to Cycas revoluta : First Report Worldwide.

A dieback was observed on three-year-old pot-grown plants of in Sicily (Italy). Symptoms, including stunting, yellowing and blight of the leaf crown, root rot and internal browning and decay of the basal stem, closely resembled the Phytophthora root and crown rot syndrome, common in other ornamentals. Isolations from rotten stem and roots, using a selective medium, and from rhizosphere soil of symptomatic plants, using leaf baiting, yielded three species, , and , were obtained. Isolates were identified by both morphological characters and DNA barcoding analysis, using three gene regions: ITS, and COI. was the sole species isolated directly from the stem and roots. The pathogenicity of the isolates of the three species was tested on one-year-old potted plants of , using both stem inoculation by wounding, and root inoculation through infested soil. was the most virulent and, like , reproduced all the symptoms of natural infections, while was the least virulent and induced solely very mild symptoms. was identified as the causal agent of the decline of , as it was re-isolated from both the roots and stems of artificially infected symptomatic plants, thus fulfilling Koch's postulates.