Phoma odoratissimi Q. Chen, 2015

Chen, Qian, Zhang, Ke, Zhang, Guozhen & Cai, Lei, 2015, A polyphasic approach to characterise two novel species of Phoma (Didymellaceae) from China, Phytotaxa 197 (4), pp. 267-281 : 274

Phoma odoratissimi Q. Chen , sp. nov. ( Fig. 2 )

MycoBank: MB 811014

Etymology: named after the species name of the host plant, Viburnum odoratissimum .

Pathogenic, leaf spot irregular or angular shape, light grey in the center with dark brown margin and red to brown coloration on the front side of leaf tissue. Pycnidia solitary or aggregated, produced on the agar surface, subglobose to broadly ellipsoidal, glabrous or with some hyphal outgrows, olivaceous buff, 155–275 (–395) × (90–) 170–235 μm. Ostioles single, slightly papillate or non-papillate. Pycnidial wall pseudoparenchymatous, composed of oblong to isodiametric cells, outer cell layer brown pigmented, 4–6 layers, 14–21 μm thick. Conidiogenous cells phialidic, hyaline, simple, smooth, ampulliform to doliiform, 3.5–6 × 4–6 μm. Conidia ellipsoidal to cylindrical, thin-walled, smooth, hyaline, aseptate, (4.5–) 5–8 × (2.5–) 3–5 μm (x =3.7 ± 0.7 × 6.5 ± 1.0, n=30), with (0–) 2–8 guttules. Conidial matrix light salmon.

Culture characteristics: Colonies on OA, 49–59 mm diam after 7 d, margin regular, densely covered by floccose, white aerial mycelia; reverse pale grey to white with some dark green near the center. Abundant black pycnidia visible after 18 d, scattered over the medium. Colonies on MEA 57–60 mm diam after 7 d, margin regular, covered by felty aerial mycelium, white to light salmon, sometimes yellowish-brown to brown around the center as concentric circle; reverse concolourous. Colonies on PDA, 46–60 mm diam after 7 d, margin regular, aerial mycelium floccose, white to grey green with isabelline near the center, pale grey with olivaceous-grey tinges near the colony margin; reverse greenish brown, salmon near the margin. Application of NaOH did not have any effect.

Specimens examined: CHINA. Hubei ; Shennongjia forest region, on diseased leaves of Viburnum odoratissimum Ker , 01 August 2011, K. Zhang (HMAS 245745!, holotype), ex-type culture CGMCC 3.17488 (= LC 1613) ; ibid. CGMCC 3.17501 (= LC 1615) ; ibid. LC 1614 ; ibid. LC 1616 ; ibid. LC 1617. CHINA. Beijing, Botanic garden, on diseased leaves of Syringa oblate Lindl. , 3 September 2012, X.B. Du, culture CGMCC 3.17502 (= LC 4742) .

Notes: Phoma odoratissimi was isolated from Viburnum odoratissimum ( Adoxaceae ), and Syringa oblate ( Oleaceae ), both of which are commonly cultivated ornamentals with long history in China and other Asian countries e.g. Korea, Thailand and so on (Li Z.G. et al. 2006). In the USDA database ( Farr et al. 2014), Phoma exigua var. viburni (Roum. ex Sacc.) Boerema (current name Boeremia exigua var. viburni Aveskamp, Gruyter & Verkley, Aveskamp et al. 2010 ), P. opuli Thüm. , P. viburnicola Oudem , have been recorded from Viburnum , and P. exigua var. lilacis (Sacc.) Boerema (current name B. exigua var. lilacis Aveskamp, Gruyter & Verkley, Aveskamp et al. 2010 ) from Syringa . Phoma odoratissimi is thus far the first report of Phoma species on Viburnum odoratissimum and Syringa oblata . Boeremia exigua var. viburni and B. exigua var. lilacis clustered in Boeremia clade ( Didymellaceae ) with other Boeremia species and are distant from P. odoratissimi in the preliminary analysis of LSU and ITS sequences (data not shown). Phoma odoratissimi differs from P. opuli in producing longer conidia (5–8 × 3–5 μm vs. 5 × 4–4.5 μm) ( Thümen 1881). Phoma odoratissimi produces pycnidia on the surface of medium and conidia usually with 2–8 guttules, while pycinidia of P. viburnicola are usually immersed and the conidia do not contain guttules ( Oudemans 1901). In multi-locus phylogenetic tree ( Fig. 1 ), P. odoratissimi clustered as a sister clade to P. bulgarica (99% identity in ITS, 93% identity in TUB). In morphology, pycnidia of P. bulgarica proved to be sterile (Avemskamp et al. 2010), while P. odoratissimi produces abundant pycnidia containing large number of conidia.

Figures

FIGURE 1. Phylogenetic tree generated from a maximum parsimony analysis based on the combined ITS, LSU, TUB and RPB2 sequence alignment. Values above the branches represent parsimony bootstrap support values (>50%). Thickened branches represent significant Bayesian posterior probability (≥95%). Novel sequences are printed in bold and the scale bar indicated 40 changes. The tree is rooted with Phoma paspali (CBS 560.81). An asterisk (*) indicates the ex-type strains.

FIGURE 2. Phoma odoratissimi (CGMCC 3.17488).A–B. Colony on OA (front and reverse). C–D. Colony on MEA (front and reverse). E–F. Colony on PDA (front and reveres). G. Lesions on diseased leaves of Viburnum odoratissimum. H–I. Pycnidia on OA. J. Section of the pycnidial wall. K. Conidia. Scale bars: I = 100 μm; J–K = 10 μm.