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 Add this item to the list  804533 Original description
   
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Page number:172 
Remarks (internal):Phytophthora virginiana was recovered from nursery irrigation water. This new species has unique morphological and physiological attributes as well as molecular signature, so that it can be readily distinguished from all known Phytophthora species. It is the only species that is heterothallic, grows well at 35°C, and produces abundant lateral chlamydospores. Phytophthora insolita (Ann & Ko 1980), which also grows well at 35°C and produces abundant thinwalled chlamydospores, is homothallic and produces terminal chlamydospores. Phytophthora lateralis (Tucker & Milbrath 1942) and P. quininea (Crandall 1947) also produce abundant lateral chlamydospores but are homothallic and did not sustain growth at 35°C (Tucker & Milbrath 1942, Crandall 1947). Phytophthora quininea also produces intercalary chlamydospores (Crandall 1947) whereas P. virginiana does not. Among the known heterothallic, high-temperature tolerant species that grow well at 35°C, only P. virginiana produces abundant lateral chlamydospores. Phytophthora melonis, P. hydrogena, and P. irrigata do not produce chlamydospores in fresh agar media (Ho et al. 2007, Hong et al. 2008, Yang et al. 2014). Some isolates of P. drechsleri were reported to produce much smaller chlamydospores (diam. 7.9 µm) (Erwin & Ribeiro 1996) than those of P. virginiana (diam. 43.5 µm). Phytophthora hydropathica and some P. parsiana isolates frequently produce chlamydospores in fresh cultures (Hong et al. 2010, Mostowfizadeh-Ghalamfarsa et al. 2008). However, these two species produce mostly terminal chlamydospores, which are rare in P. virginiana. The average chlamydospore sizes of P. hydropathica (diam. 37 µm) and P. parsiana (diam. 27-37.5 µm) are also smaller than that of P. virginiana. Additionally, the ITS sequence of P. virginiana differs from its two closely related species by 26 bp (P. hydropathica) and 39 bp (P. parsiana). This sequence difference is another important criterion for separating P. virginiana from all other existing Phytophthora species.
The phylogenetic placement of P. virginiana provides further evidence to the argument that there is a high-temperature tolerant cluster (Fig. 1) in clade 9 of the genus Phytophthora (Yang et al. 2014). Phytophthora virginiana and all other species within this unique cluster grow well at 35°C and some survive at 40°C (Fig. 2). To date, species belonging to this cluster have been found on several continents including Europe, North America, South America, and Asia. Phytophthora polonica was first described in Poland (Belbahri et al. 2006). Irrigation reservoirs in Virginia contain diverse species belonging to this cluster including P. aquimorbida (Hong et al. 2012), P. hydropathica (Hong et al. 2010), P. hydrogena (Yang et al. 2014), P. irrigata (Hong et al. 2008), and this new species P. virginiana. Phytophthora chrysanthemi, P. insolita and P. parsiana were first reported from Asia (Ann & Ko 1980, Mostowfizadeh-Ghalamfarsa et al. 2008, Naher et al. 2011). Also, a provisional species belonging to this cluster, Phytophthora sp. “lagoariana,” recovered from the Amazonian rainforest, also grows well at 35°C (data not shown). The unique correlation between physiological and phylogenetic characteristics indicates that these high-temperature tolerant species may originate from tropical or subtropical environments, and increasing international trade may have contributed to current global distribution of these species.
The ecological and economic impacts caused by P. virginiana are not clear at this time. All isolates were recovered from irrigation water at several ornamental plant nurseries in Virginia by baiting. However, plants diseased by P. virginiana have not been observed at the same nurseries. This does not necessarily mean that P. virginiana will not cause severe damage when introduced to new environments. Investigations into its host range and ecological roles inirrigation systems are warranted.
 
Description type:Original description 
Description:Phytophthora virginiana Xiao Yang & C.X. Hong, sp. nov. Fig. 4
MycoBank MB 804533
Differs from Phytophthora hydropathica by abundant, thin-walled, lateral
chlamydospores.
Type: USA, Virginia, baited with camellia leaves from irrigation water of an irrigation runoff reservoir in a production perennial nursery, October 2007, collected by Chuanxue Hong. Holotype, ATCC MYA-4927; ex-type culture, 46A2 (GenBank KC295544).
Sporangia produced occasionally by aged cultures grown on carrot agar and 20% clarified V8 juice agar, and abundantly by culture plugs submerged in 1.5% soil water extract under light within 10 hours. Sporangial shape mostly ovoid to obpyriform and sometimes limoniform to ellipsoid with distortedshaped sporangia such as peapod-shaped and peanut-shaped on culture plugs submerged in SWE after 20 hours. Sporangia terminal, nonpapillate and noncaducous; av. 51.7 x 32.5 µm. Internal proliferation of sporangiophore common, nested or extended. Sporangiophore erect, unbranched with occasional swelling. Hyphal swellings common, often peanut-shaped, angular, or variously distorted in shapes. Chlamydospores abundant, thin-walled, spherical and lateral produced by mature cultures av. 43.5 µm diam, sometimes on short stalks, with tapered base or clustered. Terminal chlamydospores rare. Phytophthora virginiana is self-sterile, producing no sexual organ in single cultures. In the polycarbonate membrane tests, P. virginiana isolates belong to silent A1 mating type, producing no sexual organ after up to 90-day-pairing, but stimulating A2 mating type isolates of P. cinnamomi and P. cryptogea to produce gametangia after 30-day-pairing at 20, 25°C and room temperature (c. 23°C).
 
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