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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 Scale bar indicates number of substitutions per site.(Martin, Blair and Coffey, unpublished).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 multivesiculata Ilieva, Man in 't Veld, W. Veenb.-Rijks & R. Pieters 1998 (Oomycetes, Pythiales)
Distribution: Europe (the Netherlands, type).
Substrate: Leaves, stems, base of bulbs.
Disease Note: Leaf and stem rot, bulb rot.
Host: Cymbidium sp. (Orchidaceae).
Supporting Literature:
Ilieva, E. , Man in 't Veld, W.A., Veenbaas-Rijks, W., and Pieters, R. 1998. Phytophthora multivesiculata, a new species causing rot in Cymbidium. Eur. J. Pl. Pathol. 104: 677-684
Updated on Jun 27, 2006
Phytophthora multivesiculata Ilieva, Man in ‘t Veld, Veenbaas-Rijks et Pieters was initially isolated from blackened leaves and stems of infected Cymbidium plants. It is a clade 2 species located in a basal position.
1. Sporangia
All isolates readily formed sporangia on solid as well as in liquid media, although more abundant in the latter. Sporangia were mainly ovoid and occasionally obpyriform, non-papillate and semi-papillate; rarely two apices were noticed. In many sporangia, residual globules and ‘papilla like’ prolongations were observed . These ‘papillate’ sporangia usually germinated with a germ tube, forming new sporangia. Most sporangia had a rounded base, occasionally a tapered base, although not as often as in the P. porri isolates used for comparison. Laterally attached sporangia were also present. Sporangia dimensions varied considerably within one isolate but there were no significant differences between isolates. Summarized data of all isolate dimensions are: 30–60 X 20–41 µm (av. 45 X 33 µm) with length:breadth ratio 1.10–1.78 (av. 1.43); exit pore 8.0–14.0 µm (av. 10 µm). Sporangia usually were produced singly on long, slender, mainly twisted sporangiophores, but sympodial arrangement of sporangia up to 3 was common on both solid and liquid media. Internal proliferation of sporangia was observed in water cultures in all isolates, more readily in isolate PD 94/830. Sometimes hyphal swellings were observed beneath the sporangium.
2. Chlamydospores
Not observed
3. Sex Organs
Sexual structures of P. multivesiculata were produced on both agar and in liquid media as well as in plant tissues, where they were formed in groups. Oogonia were spherical, smooth-walled; dimensions on V8 were 28.0–50.0 µm (av. 41 µm). Oospores mainly aplerotic; dimensions 24.0–42.0 µm (av. 33.0 µm). No significant differences in dimensions of oogonia, oospores and antheridia were observed between isolates. Antheridia were irregularly spherical or ellipsoidal, sometimes prolongation of hyphae was present. Antheridia were mostly amphigynous (95%) and some diclinous.
4. Growth Temperatures
Maximum of 35° C.
5. Growth Characteristics in Culture
Colonies on V8, PDA, OA and CA exhibited moderately fluffy aerial mycelium, a little denser in the middle of the colony on PDA; on CMA mycelium was essentially submerged. On V8 the colony of P. megasperma (PD 94/118) had more aerial mycelium with irregular growth, the colony of P. porri (PD 92/214) showed dense low aerial mycelium with a powdery appearance and many coiled hyphae, easily observed on the reverse side of the colony.
6. Distinguishing Characteristics
Having semi-papillate to non-papillate sporangia, and mainly amphigynous antheridia, P. multivesiculata can be classified as a group IV species. P. multivesiculata can easily be distinguished from the other group IV species, because it is the only one which has a maximum temperature for growth of 35° C and forms catenulate hyphal swellings in both solid and liquid media. A conspicuous feature of P. multivesiculata is the internal proliferation of sporangia, which is a characteristic feature of groups V and VI. However, of all group V and VI species, only P. humicola, P. richardiae and P. insolita form catenulate hyphal swellings on agar and of these only P. insolita has a high maximum temperature for growth (38° C), which is significantly higher than recorded for P. multivesiculata. Moreover, oogonia are larger in P. multivesiculata than in P. insolita, chlamydospores are observed in P. insolita but not in P. multivesiculata and antheridia, present in P. multivesiculata, are lacking in P. insolita. Superficially the features of P. multivesiculata resembled features of both P. porri and P. megasperma. A closer examination, however, revealed small but marked differences with these species. P. porri, so far only known to be pathogenic to the genera Allium and Brassica, has a typical slow growth and low optimum and maximum growth temperatures. P. multivesiculata shows considerably higher growth rates at 20° C than P. porri, but lower than those observed for P. megasperma. The maximum temperature for growth of P. multivesiculata is 35° C. Catenulate hyphal swellings, typical for P. multivesiculata, are observed in P. porri occasionally, but their appearance in this species is mainly rounded with more radiating hyphae. P. porri isolates formed sporangia often with a tapered base and never with internal proliferation. Sporangia formation of P. megasperma isolates was observed only in water culture whereas internal proliferation was more common than in P. multivesiculata. In P. porri and P. megasperma isolates mostly paragynous antheridia were observed.
Naturally infected Cymbidium plants showed dry rot of leaves (with a somewhat waxy looking surface) with a change of color to brown with typical horizontal zebra-like stripes, about 0.5 cm wide with lighter discoloration in the middle and a dark brown to black margin. The base of the Cymbidium bulbs showed wet brown-black discolored tissue. On artificially inoculated Cymbidium leaves, symptoms became visible after 6 days. Dry brown rot was observed, but the typical zebra-like stripes were less conspicuous.
Ilieva, E., Man in ’t Veld, W.A., Veenbaas-Rijks, W. and Pieters. R. 1998. Phytophthora multivesiculata, a new species causing rot in Cymbidium. Eur. J. Plant Pathol. 104: 677–684
Nomenclature information was provided by the the Systematic Botany and Mycology Laboratory in USDA-ARS. This species page was adapted from Illieva et al. (1998).
Isolate list