Epitypification of Ceratocystis fimbriata

Abstract

Ceratocystis accommodates many important pathogens of agricultural crops and woody plants. Ceratocystis fimbriata, the type species of the genus is based on a type that is unsuitable for a precise application and interpretation of the species. This is because no culture or DNA data exist for the type specimen. The aim of this study was to select a reference specimen that can serve to stabilize the name of this important fungus. We selected a strain, CBS 114723, isolated from sweet potato in North Carolina, USA, in 1998 for this purpose. The strain was selected based on the availability of a living culture in a public depository. A draft genome sequence is also available for this strain. Its morphological characteristics were studied and compared with the existing and unsuitable type specimen as well as with the original descriptions of C. fimbriata. The selected strain fits the existing concept of the species fully and we have consequently designated it as an epitype to serve as a reference specimen for C. fimbriata.

Keywords: Ceratocystidaceae; Ipomoea batatas; Microascales; nomenclature.

Fig. 1.

Specimen pouches and contents linked to Ceratocystis fimbriata. A–C. Superseded neotype (BPI 595863). D, E. Holotype (NY 01050464). A. Envelope containing the specimen designated as neotype. B. An original note in the pouch. C. Black rot (circles) on stolons of sweet potato. D. Envelope containing the holotype specimen. E. Sweet potato peels. (Images D, E are from http://sweetgum.nybg.org/images3/1700/343/01050464.jpg).

Fig. 2.

Ceratocystis fimbriata infecting a sweet potato. A–C. Drawings from Halsted (1890). D–H. Sweet potato tuber inoculated with C. fimbriata (Ex-epitype, CBS 114723). I–M. Superseded neotype (BPI 595863) of C. fimbriata. A. Sweet potato and young shoot showing the black rot symptom. B. Ascomata with a long neck exuding a slimy droplet of spores at its tip, and the ascomatal base embedded in the substrate. C. Aleuriospores and their conidiophores, and thielaviopsis-like conidia (marked as ‘d’). D, E. Sweet potato showing fully developed black-rot lesions 2 wk after inoculation. F. Ascomata on young shoot. G. Ascomata produced in the lesion on the surface of the tuber. H. Close-up of ascomata with a slimy droplet of ascospores. I. Ascomata (circle) with broken necks in dried shoot. J. Pigmented thielaviopsis-like conidiophores. K. Aleuriospores. L, M. Thielaviopsis-like conidia. Scale bars: F = 250 μm; I = 1 mm; G, H = 200 μm; J, K = 10 μm; L, M = 5 μm.

Fig. 3.

Microscopic features of Ceratocystis fimbriata growing on sweet potato broth agar medium (SPA). A, C, E, G, L, O, Q: Drawings of Halsted & Fairchild (1891). B, D, F, H–K, M, N, P, R–T: Images of the ex-epitype (CBS 114723). A, B. Ascoma. C, D. Divergent ostiolar hyphae. E, F. Clustered ascospores. G–K. Ascospores (K focused on a sheath of J). L–N. Aleuriospores in chains. O, P. Thielaviopsis-like conidia. Q–T. Thielaviopsis-like conidia in chains. Scale bars: B = 100 μm; D = 25 μm; F, M, N, P, R–T = 10 μm; H–K = 2.5 μm.

Fig. 4.

Ceratocystis fimbriata and closely related species in Ceratocystis. One of the most parsimonious trees selected from maximum parsimony analysis of ITS sequence data of Ceratocystis fimbriata from Ipomoea batatas, and closely related species. Bootstrap support values above 60 % are indicated above or below branches. The ex-epitype or ex-type strain is indicated by ET or T, respectively.