Phoma segeticola 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 : 274-277

Phoma segeticola Q. Chen , sp. nov. ( Fig. 3 )

MycoBank: MB 811015

Etymology: named after the species name of the host plant, Cirsium segetum .

Pathogenic, leaf lesions irregular, polygonal, pale grey in center, surrounded by significant dark brown to black margin. The spots enlarge and merge, while the plant tissues near the lesions become yellow as the diseases progress. Pycnidia solitary to confluent, subglobose, glabrous, on the agar surface. Later developing to pyriform to irregular shaped with many hyphal outgrows and with a clear neck around the ostioles, forming an irregular shape, (75–) 90–105 × 75–95 (–112) μm. Ostioles 1–2, on an elongated neck. Pycnidial wall pseudoparenchymatous, composed of oblong to isodiametric cells, 3–5 layers, 9.5–15.5 (–22.5) μm thick. Conidiogenous cells phialidic, hyaline, simple, smooth, flask-shaped or sometimes isodiametric, 5–6.5 × 4–5.5 μm. Conidia ellipsoidal to ovoid or cylindrical, thin-walled, smooth, hyaline, aseptate, 4.5–7 × 2.5–4 μm (x =2.9 ± 0.5 ×5.0 ± 1.0, n=30), with 1–6 polar guttules. Conidial matrix crème-white.

Culture characteristics: Colonies on OA, 56–65.5 mm diam after 7 d, margin regular, aerial mycelium woolly, white to grey; reverse gray olivaceous. Abundant black pycnidia on the colony surface. Colonies on MEA, 64–66 mm diam after 7 d, margin regular, covered by a floccose cream mat of white aerial mycelium, with greenish grey near the center; reverse concolourous. Colonies on PDA, 52–59 mm diam after 7 d, margin regular, aerial mycelium felt to compact, initially white, later developing to iron-grey tufts occur near the center; reverse dark olivaceous to dark brown. NaOH test negative.

Specimens examined: CHINA. Hubei ; Shennongjia forest region, on diseased leaves of Cirsium segetum Bunge , 01 August 2011, K. Zhang (HMAS 245746!, holotype), ex-type culture CGMCC 3.17489 (= LC 1636) ; ibid. CGMCC 3.17498 (= LC 1635) ; ibid. LC 1633 ; ibid. LC 1634 .

Notes: Cirsium segetum is one of the edible wild herbs commonly known as thistles in the Asteraceae . Several species of Phoma sensu lato have been reported on Cirsium plants, including P. cirsii Dietel & P. Syd. , P. exigua Desm. var. exigua (current name Boeremia exigua var. exigua (Desm.) Aveskamp, Gruyter & Verkley, Aveskamp et al. 2010 ), P. macrostoma Mont. var. macrostoma , P. nebulosa (Pers.: Fr.) Berk., P. pycnocephali Pass. , P. rubella Cooke and P. tropica R. Schnerd. & Boerema ( Farr et al. 2014). Boeremia exigua var. exigua and Phoma tropica clustered in separate branches distant from P. segeticola in the phylogenies of LSU and ITS (data not shown); P. macrostoma var. macrostoma and P. nebulosa clustered in two different clades distinct from P. segeticola in multi-locus phylogenetic tree ( Fig. 1 ). In morphology, Phoma segeticola differs from P. cirsii in its smaller pycinidia (90–105 × 75–95 μm in P. segeticola vs. 180 μm in P. cirsii ) ( Dennis 1986); from P. rubella and P. pycnocephali in its wider conidia (4.5–7 × 2.5–4 μm in P. segeticola vs. 7 × 2 μm in P. rubella , 5 × 1–1.5 μm in P. pycnocephali ) ( Cooke 1885, Saccardo 1892). Phoma segeticola is the first record of Phoma species on Cirsium segetum . The ex-type of P. segeticola (CGMCC 3.17489) showed close phylogenetic relationship with P. bellidis (100% identity in ITS, 98% identity in TUB, 96% identity in RPB2) and P. senecionis (99% identity in ITS, 95% identity in TUB). These three species were all found in association with different genera of the plant family Compositae ( Boerema et al. 2004) . The conidia of Phoma segeticola are slightly wider (4.5–7 × 2.5–4 μm) than P. bellidis (4–6.5 × 2–2.5 μm) and P. senecionis (4–6.5 × 1.5–2.5 μm) ( Boerema et al. 2004). The colony of P. segeticola on OA was better developed with aerial mycelium, and the NaOH test showed negative result. While for P. bellidis and P. senecionis , aerial mycelium were poorly developed and the application of NaOH drop showed positive reaction ( Boerema et al. 2004).

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 3. Phoma segeticola (CGMCC 3.17489). A–B. Colony on OA (front and reverse). C–D. Colony on MEA (front and reverse). E–F. Colony on PDA (front and reverse). G. Lesions on diseased leaves of Cirsium segetum. H–J. Pycnidia on OA. K. Longitudinal section of the pycnidium. L. Section of the pycinidal wall. M. Conidia. Scale bars: H, J = 50 μm; I = 100 μm; K–M = 10 μm.