New Phytophthora species: Phytophthora niederhauserii
The NPPO of Spain informed the EPPO Secretariat that at the end of summer 2007 a severe decline of 2 year-old almond trees (Prunus dulcis) was noticed in 1 nursery in Valencia province (Comunidad Valenciana). Affected trees developed small chlorotic leaves, wilted and finally died showing cankers and gum exudation on the stems. A Phytophthora species was consistently isolated from the stems and roots of infected trees. The isolates obtained did not fit the morphological description of any described Phytophthora species but they were similar to other Spanish isolates obtained in 2001 from Cistus monspeliensis and C. salvifolius, and in 2005 from Hedera sp. (see also EPPO RS 2009/163). Sequence analysis of the ITS region of rDNA was performed and compared with other sequences deposited in the GenBank database. The ITS sequence showed high similarity with Phytophthora niederhauserii.
Although it has not yet been formally described, Phytophthora niederhauserii was reported as a new species in 2003 on Thuja occidentalis and Hedera helix plants grown in glasshouses in North Carolina (US). Since this initial discovery, P. niederhauserii has been reported from different continents on different plant species. In the USA, it was found in 2007 on Ceanothus sp. in the county of Santa Barbara, California. In Australia, P. niederhauserii has been detected on imported nursery plants and in natural ecosystems on Banksia prionotes. In Europe until its detection in almond trees, it was mainly detected in nurseries on ornamental plants grown in containers. In Sicilia (IT), P. niederhauserii was detected in spring 2003 on potted plants of Callistemon citrinus and Cistus salvifolius showing leaf chlorosis, defoliation and wilt associated with root and collar rot. On the mainland, it has also been reported from potted plants of Banksia speciosa. In Norway, P. niederhauserii has been detected on Begonia hybrids, Hedera helix, Kalanchoe blossfeldiana, Sinningia speciosa, and Peperomia clusiifolia. Symptoms included root and stem necrosis. On H. helix and S. speciosa, wilting of the whole plant was observed; on Kalanchoe, only root discoloration and reduced plant growth were seen. Finally in the United Kingdom, P. niederhauserii was detected on Cistus sp. grown under glasshouse conditions. Although further studies are needed to characterize P. niederhauserii and better understand its biology, this illustrates once more the necessity to build appropriate management strategies in nurseries to avoid the development and spread of Phytophthora diseases.
Sources
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