Bretziella fagacearum (Bretz) Z.W.deBeer, Marinc., T.A.Duong & M.J.Wingf., 2017

Beer, Z. Wilhelm de, Marincowitz, Seonju, Duong, Tuan A. & Wingfield, Michael J., 2017, Bretziella, a new genus to accommodate the oak wilt fungus, Ceratocystisfagacearum (Microascales, Ascomycota), MycoKeys 27, pp. 1-19 : 4-5

Bretziella fagacearum (Bretz) Z.W.deBeer, Marinc., T.A.Duong & M.J.Wingf. comb. nov. Figures 2, 3

Bas.: Endoconidiophora fagacearum Bretz, Phytopathology 42: 436. 1952; Ceratocystis fagacearum (Bretz) Hunt, Lloydia 19: 21. 1956. TYPES: USA. Dry culture resulting from a cross between two isolates, locations unknown, from Quercus sp., 26 Feb 1952, T.Bretz (Lectotype designated here: FP 97476, MycoBank typification number: MBT 378423). USA. Iowa, on Quercus rubra , 1991, S.Seegmueller (Epitype designated here: BPI 893238, MycoBank typification number: MBT 378424; ex-epitype culture CBS 138363 = CMW 2656). Representative sequences from epitype: 60S = KM495518, LSU = KM495341, MCM7 = KM495430, ITS = KU042044, TEF1α = KU042043. See Notes 1, 2 and 3 below.

= Chalara quercina Henry, Phytopathology 34: 633. 1944; Thielaviopsis quercina (Henry) A.E.Paulin, T.C.Harr. & McNew, Mycologia 94: 70. 2002. TYPE: USA. Dry culture, Wisconsin, Madison, on Quercus sp., Sept. 1943, B.Henry (Lectotype designated here: BPI 595712, MycoBank typification number: MBT 378425). See Note 4 below.

Descriptions.

Henry (1944, pp. 631-635, Figure 1); Bretz (1951, p. 298, Figure 1); Bretz (1952, p. 436-437, Figure 1); Stessel and Zuckerman (1953, pp. 65-67, Figure 1); Hunt (1956, p. 21); Nag Raj and Kendrick (1975, pp. 94, 131, figure 32A); Upadhyay (1981, p. 66).

Note 1.

Based on the one fungus one name principles adopted in the Melbourne Code ( Hawksworth 2011, McNeill et al. 2012), the older basionym of the oak wilt pathogen, Chalara quercina ( Henry 1944), has nomenclatural priority over Endoconidiophora fagacearum , the name Bretz (1952) assigned to the sexual state of the fungus. However, since Hunt (1956) treated the fungus as Ceratocystis fagacearum , the latter name were given preference under the dual nomenclature system in all major taxonomic works on the genus to date ( Griffin 1968, De Hoog 1974, Nag Raj and Kendrick 1975, Upadhyay 1981, Seifert et al. 1993, Paulin-Mahady et al. 2002, Harrington 2009, De Beer et al. 2013 b, 2014, Wingfield et al. 2013, Mayers et al. 2015). During the course of the past approximately 60 years, the name Ceratocystis fagacearum has also been adopted by plant pathologists and mycologists working on all aspects of the important disease known as oak wilt and the biology of the fungus (e.g. Shigo 1958, Cobb et al. 1965, Peplinksi and Merrill 1974, Gibbs and French 1980, Juzwik and French 1983, Appel et al. 1990, Kile 1993, Gibbs 2003, Juzwik et al. 2008, 2011). A search on 26 August 2017 for C. fagacearum in Google Scholar and Google respectively yielded 1940 and 119000 hits, while the name Ch. quercina yielded only 431 and 3330 hits respectively. This provides strong evidence that C. fagacearum is the more 'widely used’ name (see Hawksworth 2012).

In the present study, we have shown that the oak wilt fungus does not belong in Ceratocystis s. str., Endoconidiophora , Thielaviopsis or any of the other genera currently accepted in the Ceratocystidaceae ( De Beer et al. 2014, Mayers et al. 2015). We have consequently suggested that it is treated in a novel genus for which we have provided the name Bretziella . Based on the widespread use of the name C. fagacearum , we submitted a formal proposal that its basionym, Endoconidiophora fagacearum , is conserved against Chalara quercina (= Thielaviopsis quercina ), to enable the new combination, Bretziella fagacearum , proposed above.

Note 2.

In the protologue of E. fagacearum , Bretz (1952) specified the location of the holotype as 'Type, For. Path. 97476, deposited in the Mycological Collections of the Bureau of Plant Industry, Soils and Agricultural Engineering’. In subsequent studies, the holotype specimen was referred to as 'BPI-FP 97476' ( Hunt 1956, Nag Raj and Kendrick 1975, Upadhyay 1981). BPI has confirmed to us that this specimen had been lost. Fortunately, another specimen with the same number (FP 97476) as the one used in the protologue, was recently discovered in the Centre for Forest Mycology Research Herbarium USDA-FS-NRS (FP) and was made available for this study. This specimen included a note by T. Bretz dated 26 Feb. 1952, marked as ‘type’. It is thus clear that this specimen represents an isotype of E. fagacearum . Based on Art. 9.12 ( McNeill et al. 2012), we designate FP 97476 as lectotype for E. fagacearum .

Note 3.

The lectotypes designated here for Ch. quercina and E. fagacearum both consist of dried specimens for which DNA sequence data are not available. However, based on careful microscopic comparisons between these two specimens and a living isolate from Iowa (Figure 2), we have concluded that the specimens and isolate all represent the same species. Although Bretz (1951, 1952) did not specify the host and location of the (now) lectotype of E. fagacearum , he stated that ascomata were obtained from multiple crosses between isolates from several Quercus spp. and Chinese chestnut ( Castanea mollissima ) occurring in Missouri, Arkansas, Ohio, Michigan, Pennsylvania, West Virginia, Kentucky, Tennessee, North Carolina, and Virginia. The specimen of Henry (1944) came from an unnamed Quercus sp. in Wisconsin, but he also included isolates from several Quercus spp. in Illinois, Iowa, and Minnesota in his study. Thus, although our living isolates do not come from the same host species and location as the lectotypes, they originate from the same host genus and geographical area (Midwest and Eastern States) from where isolates have been included in the studies of Henry (1944) and Bretz (1951, 1952). Based on the morphology, host, and origin, we have designated a dried culture of one of our isolates as epitype for E. fagacearum to enable the inclusion of the oak wilt fungus in DNA based studies.

Note 4.

Henry (1944) lodged the original specimens of Chalara quercina in two collections but did not designate either as the holotype. One of these specimens (BPI 595712 = FP 94260) was included in the present study and is designated here as lectotype.