Name and publication
Phytophthora heterospora Scanu, Cacciola, Linaldeddu & Jung (2021)
Scanu B, Jung T, Masigol H, Linaldeddu BT, Jung MH, Brandano A, Mostowfizadeh-Ghalamfarsa R, Janoušek J, Riolo M, Cacciola SO. 2021. Phytophthora heterospora sp. nov., a new pseudoconidia-producing sister species of P. palmivora. Journal of Fungi 7: 870.
Type: Italy, Sardinia, Sorso, from a bark lesion on a young olive tree, 2010, collected by B. Scanu type CBS H-24777
Ex-type: culture CBS 148034 = PH054
Sequences for ex-type in original manuscript: CBS 148034 = PH054; ITS MT232393, β-tubulin MZ782807, cox1 MZ782828, HSP90 MZ782849
Position in ITS phylogenetic tree
Colonies and cardinal temperatures
Colony morphology radiate with limited aerial mycelium on CA and V8A, uniform and slightly woolly on PDA, and poorly developed, dense-felty with irregular margin on MEA. Minimum growth temperature 12°C, optimum 27.5°C, and maximum 32.5°C.
Conditions for growth and sporulation
Sporangia and pseudoconidia are produced in water cultures (soil extract) and in solid media. Oogonia are formed readily when paired with known A1 and A2 tester strains of P. cinnamomi and P. palmivora on CA about 20 days.
Sporangia were papillate, caducous with a short pedicel <5 μm, and predominantly ovoid in shape with external proliferation. Sporangia averaged 42.8 × 24.7 µm (overall range 15.6–72.6 x 12.4–42 µm); Sporangiophores simple or loose sympodia. Pseudoconidia were caducous and predominantly ellipsoid in shape with external proliferation at base forming monochasial helicoid sympodia. They do not produce zoospores but germinate directly. Pseudoconidia dimension averaged 34.7 × 27.1 μm (overall range 24.0–44.2 × 16.5–27.1 μm).Hyphal swellings present. Chlamydospores present, abundant.
Heterothallic. Oogonia had smooth walls and often with a short tapering base, size ranged from 24.3–37.4 µm. Oospores aplerotic, size ranged 20.2–31.4 µm. Oospores often aborted after formation of the walls. Antheridia amphigynous.
Most typical characters
Phytophthora heterospora is a sister species to P. palmivora but differs by the production of pseudoconidia on solid agar media. Other key differences are the lower maximum temperature for growth and faster growth rates at most temperatures of P. heterospora and the higher oospore abortion rate of P. heterospora. Many sequences submitted to Genbank as P. palmivora are identical to P. heterospora.
Additional specimen(s) evaluated
ITALY, Sardinia, Villamar, from Olea europaea, 2010, B. Scanu, CBS 148035 = PH051; PH052; PH057; Sorso. PH047; Sicily, Catania, from Capparis spinosa, 2014, S.O. Cacciola, CBS 148036 = 317-A12; Campobello di Mazara, from Olea europaea, 2005, Campobello 2b; Calabria, Lamezia Terme, from Olea europaea,1999, Palm2. Vietnam, Mekong Delta, Vinh Long, necrotic bark lesions on Durio zibethinus trees, 2013, S.O. Cacciola, DB2; A1A; A1B1; C2B1
Hosts and distribution
Distribution: Italy, Iran, Vietnam
Substrate: stems and roots
Disease note: stem lesions, root and collar rot of young olive trees
Host: Olea europaea, Ziziphus spina-christi, Juniperus oxycedrus, Capparis spinosa, Durio zibethinus
Additional references and links
Fact sheet authors
Bruno Scano and Treena Burgess