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Genus wide phylogeny for Phytophthora using four mitochondrial loci (cox2, nad9, rps10 and secY; 2,373 nucleotides). Maximum likelihood branch lengths shown. Numbers on nodes represent bootstrap support values for maximum likelihood (top), maximum parsimony (middle) and Bayesian posterior probabilities as percentages (bottom). Nodes receiving significant support (>95%) in all analysis are marked with an asterisk (*). Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).
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Phytophthora gregata T. Jung, M.J.C. Stukely & T.I. Burgess 2011 (Oomycetes, Pythiales)
Distribution: Australia.
Substrate: Associated with roots of dying plants.
Supporting Literature:
Jung, T., Stukely, M.J.C., Hardy, G.E.St.J., White, D., and Paap, T. 2011. Multiple new Phytophthora species from ITS Clade 6 associated with natural ecosystems in Australia: evolutionary and ecological implications. Persoonia 26: 13-39.
Updated on Aug 29, 2011
P. gregata T. Jung, M. J. C. Stukely & T. I. Burgess is generally associated with dying vegetation in swampy or water-logged areas in Western Australia and Victoria. It forms a new cluster in Phytophthora clade 6 with P. gibbosa, P. taxon paludosa, P. taxon raspberry and P. taxon cranberry.
1. Sporangia
Sporangia are rarely observed on solid agar but are produced abundantly in non-sterile soil extract. . Sporangia were usually borne terminally on unbranched sporangiophores, often in chains of internally proliferating sporangia, or much less frequently in lax sympodia. Sporangia were non-caducous, nonpapillate and usually with a flat apex. Sporangial shapes ranged from usually ovoid (Fig. 1c) and less frequently limoniform ellipsoid (Fig. 1b), pyriform or obpyriform (Fig. 1a). Sporangia usually proliferated internally in both a nested (Fig. 1c) and extended way (Fig. 1d). External proliferation was not observed. In all isolates some sporangia formed numerous wall ingrowths which became clearly visible after zoospore release (Fig. 1d). Sporangial dimensions average averaged 51.0 ± 13.8 × 30.5 ± 5.9 μm (overall range 25.7–102.3 × 14.8 – 50.7 μm). The length/breadth ratio of the sporangia average 1.67 ± 0.32. Hyphal swellings were common. Inside the V8 agar and also in liquid culture, all isolates frequently produced dense hyphal aggregations formed from both clusters of lateral hyphae and the twisting of hyphae around each other (Fig. 2).
2. Chlamydospores
Chlamydospores not observed.
3. Sex Organs
P. gregata is homothallic and with the exception of one isolates, produced oogonia in single culture on V8 agar within 4 days (Fig. 3). This isolate and the others produced oogonia when paired with tester strains and other P. gregata isolates. More oogonia are produced when paired than in single culture. The average abortion rate (85%) was high in both single culture and over all pairing combinations, but varied considerably between isolates (Fig. 3d-e). None of the P. gregata isolates induced oogonia formation in the A1 and A2 tester isolates. In conclusion, the breeding system of P. gregata is homothallic or partially or sporadically self fertile.
Oogonia were borne terminally or laterally and had globose, subglobose to slightly excentric (Fig. 3c) or elongated shapes, often with a tapering base (Fig. 3c). Oogonial walls sometimes turned golden-brown while ageing. Oogonial diameters averaged 36.8 ± 4.1 μm. Oospores were usually aplerotic (Fig. 3b-d), globose and contained a large ooplast. They had a mean diameter of 31.6± 4.0 μm, thick walls (av. 2.65 ±0.81 μm) and a mean oospore wall index of 0.42 ± 0.09. Antheridia were formed terminally or laterally and were predominantly paragynous.
4. Growth Temperatures
Radial growth rates on V8 agar at optimum temperature (25 °C) was 6.5 ± 0.7 mm/d. Isolates were unable to grow at 35 °C, and did not resume growth when plates incubated for 7 d at 35 °C were transferred to 20 °C.
5. Growth Characteristics in Culture
On V8A (Fig. 4a) and carrot agar (Fig. 4b), P. gregata formed faintly striate, stellate or uniform colonies with sparse to limited aerial mycelium were formed. Colonies on MEA (Fig. 4c) and PDA (Fig. 4d) appeared woolly (more so on PDA) with a uniform or faintly stellate pattern.
6. Distinguishing Characteristics
In previous studies P. gregata is referred to as P. taxon raspberry (Brasier et al. 2003a) and P. sp. 7 (Burgess et al. 2009). It has been previously misidentified in WA as P. megasperma or P. megasperma var. sojae (Burgess et al. 2009). Phytophthora gregata can be separated from P. megasperma and other clade 6 species by the high rate of oogonial abortion and the production of extensive hyphal aggregations
7. Type isolate
AUSTRALIA, Western Australia, Busselton, from rhizosphere soil of dying Patersonia sp., 2009, VHS, holotype MURU 462 (dried culture on V8A, Herbarium of Murdoch University, Western Australia), cultures extype CBS127952 and VHS21962; ITS, ß-tubulin, HSP90, cox1 and NADH, and sequence GenBank HQ012942, JN547606, HQ012904, HQ012858 and JN547694 respectively, MycoBank MB518764.
Pathogenic on Patersonia sp., Xanthorrhoea preissii, Hakea sp.and Pinus radiata.
Burgess TI, Webster JL, Ciampini JA, White D, Hardy GESJ, Stukely MJC. 2009. Re-evaluation of Phytophthora species isolated during 30 years of vegetation health surveys in Western Australia using molecular techniques. Plant Disease 93: 215-223.
Jung, T., Stukely, M. J. C., St. Hardy, G. E., White, D., Paap, T. Burgess, T. I., 2011. Multiple new Phytophthora species from ITS Clade 6 associated with natural ecosystems in Australia: evolutionary and ecological implications. Persoonia 26: 13–39.
Brasier CM, Cooke DEL, Duncan JM, Hansen EM. 2003a. Multiple new phenotypic taxa from trees and riparian ecosystems in Phytophthora gonapodyides – P. megasperma ITS Clade 6, which tend to be high-temperature tolerant and either inbreeding or sterile. Mycological Research 107: 277–290.
This page was written by Treena Burgess, Centre for Phytophthora Science and Management, Murdoch University, Australia.
Isolate list