Colletotrichum: complex species or species ... - CBS - KNAW

The Colletotrichum acutatum species complexFig. 22. Colletotrichum paxtonii (from ex-holotype strain IMI 165753). A–B. Conidiomata. C–F. Conidiophores. G–K. Appressoria. L–M. Conidia. A, C–D, L. from Anthriscus stem.B, E–K, M. from SNA. A–B. DM, C–M. DIC, Scale bars: A = 100 µm, C = 10 µm. Scale bar of A applies to A–B. Scale bar of C applies to C–M.Stelis emarginata (syn. Physosiphon loddigesii). The collection onCymbidium appears to be effete, and while a few of the conidiomatacontained setae, no conidia or conidiogenous cells were seen. Thismay be why C. orchidearum forma cymbidii was not described inthe original publication. It is necessary to designate one of theseauthentic collections as lectotype of C. orchidearum in order to fixthe application of that name, and we therefore choose M-0140831for this purpose as M-0140830 is effete and M-0140832 is ratherdepauperate. That has the effect that C. orchidearum formaeriae becomes an obligate synonym of C. orchidearum formaorchidearum. There are no significant morphological differencesbetween the material from Eria and that from Physosiphon. Theconidiomata of the invalid forma cymbidii are substantially largerthan those of the two validly published forms, and the host plantmaterial is strongly blackened in their immediate vicinity. We areunable to establish the significance of this distinction; it may behost- rather than fungus-related.Yang et al. (2011) reviewed species of Colletotrichum fromorchids in south-western China. They identified one clade as C.orchidearum, and their Chinese strain does seem to have closesimilarities with the type of that species. None of the speciestreated in Yang et al. (2011) belong to the C. acutatum complex.Colletotrichum paxtonii Damm, P.F. Cannon & Crous, sp.nov. MycoBank MB800508. Fig. 22.Etymology: Named after Sir Joseph Paxton, gardener to WilliamSpencer Cavendish, 6 th Duke of Devonshire, who first brought theCavendish banana into cultivation.Sexual morph not observed. Asexual morph on SNA. Vegetativehyphae 1–8 µm diam, hyaline to pale brown, smooth-walled,septate, branched. Chlamydospores not observed. Conidiomatanot developed, conidiophores formed directly on hyphae. Setaenot observed. Conidiophores hyaline, smooth-walled, septate,branched, to 30 µm long. Conidiogenous cells hyaline, smoothwalled,cylindrical to ± inflated, 5–10 × 2–4 µm, opening 1–1.5µm diam, collarette 1–1.5 µm long, periclinal thickening distinct.Conidia hyaline, smooth-walled, aseptate, straight, cylindricalwith one end round and one end slightly acute both ends slightlyacute, (5–)10.5–15.5(–19.5) × (2.5–)3.5–4(–4.5) µm, mean ± SD= 13.0 ± 2.6 × 3.7 ± 0.3 µm, L/W ratio = 3.5. Appressoria singleor in loose groups, medium brown, smooth-walled, subglobose,elliptical or clavate, the edge undulate or entire, (5–)6–11.5(–16.5)× (3.5–)5.5–7.5(–8.5) µm, mean ± SD = 8.8 ± 2.7 × 6.5 ± 1.1 µm,L/W ratio = 1.4, strain CBS 502.97 forms smaller appressoria,measuring (3.5–)4.5–7.5(–10.5) × (3–)3.5–5(–5.5) µm, mean ± SD= 6.0 ± 1.7 × 4.2 ± 0.7 µm, L/W ratio = 1.4.Asexual morph on Anthriscus stem. Conidiomata acervular,conidiophores formed on pale brown, angular, basal cells 3.5–7.5www.studiesinmycology.org85