Pleosporales » Didymellaceae » Ascochyta

Ascochyta pisi

Ascochyta pisi Lib., Pl. crypt. Arduenna, fasc. (Liège) 1(nos1-100): no. 59 (1830)

            ≡ Septoria leguminum var. pisorum (Lib.) Desm., Ann.Sci. Nat. Bot., ser. 2, 19: 344. 1843.

= Didymella pisi Chilvers et al., Mycol. Res. 113: 396.2009.

Index Fungorum number: IF177968; Facesofungi number: FoF 06808

Epitype: NETHERLANDS, Venlo, from Pisum sativum, M.M.J. Dorenbosch, HMAS 246705, MBT202502, ex-epitype culture CBS 122785 = PD 78/517; isotype: BELGIUM, from pods of Pisum sativum, BR 5020059493320.                                

Saprobic on dead stem of Dioscorea communis. Sexual morph: Ascomata 100–150 × 300–350 µm (x̄ = 120 × 250 µm, n = 5), semi-immersed, solitary, globose to subglobose with long neck, uni-loculate, conspicuous and appear as black dots on host surface, shiny. Ostiole central. Ostiolar neck 100–130 µm long, 90–95 µm wide, papillate, flled with dark brown to hyaline cells. Peridium 45–60 µm wide (x̄ = 54 µm, n = 5) at the upper-most region of vertical wall, comprising of 3–5 cell layers, outermost layer composed dark brown cells of textura globulosa, inner layer composed light brown to hyaline cells of textura angularis. Hamathecium comprising numerous, 2.7–4.4 µm wide (x̄ = 3.35 µm, n = 20), flamentous, septate, pseudoparaphyses, branching and anastomosing between and above the asci. Asci 120–240 × 17–24 µm (x̄ = 149.7 × 21.4 µm, n = 15), 8-spored, bitunicate, cylindric-clavate, short pedicellate, rounded at the apex, with a conspicuous ocular chamber. Ascospores 21–49 × 8–12 µm (x̄ = 29.8 × 9.4 µm, n = 20) 1-seriate, hyaline, fusiform, 1-septate, constricted at the septum, acute at the apices, smooth, thin-walled, guttulate, lower cell is slightly wider than the upper cell. Asexual morph: Undetermined.

Material examined: ITALY, Pianetto - Galeata (province of Forlì-Cesena [FC], lives on a dead hanging stem of Dioscorea communis (L.) Caddick & Wilkin (Dioscoreaceae), 10 March 2018, Erio Camporesi, IT3777 (MFLU 18-0904, new host record), living culture MFLUCC 18-1351.

Culture characteristics: Ascospores germinating on PDA within 24 h from single spore isolation. Colonies on PDA reaching 25–30 mm diam. after one week at 16 °C, circular, entire edge, white, with dense, convex with papillate surface, brown in reverse.

Known host and distribution: Pisum sativum (Belgium, Canada, Netherlands, USA, and Washington), Dioscorea communis (Italy, Province of Forlì-Cesena), Juglans regia (Netherlands) as well as various hosts worldwide (Chilvers et al. 2009, Chen et al. 2015, Farr and Rossman 2020, Hyde et al. 2020).

GenBank numbers: ITS: MN640976, LSU: MN640975, TUB2: MN650642.

Note: Ascochyta pisi is a species complex which causes ascochyta blight disease mainly on Pisum sativum (Chilvers et al. 2009). The sexual morph of Ascochyta has been referred to Didymella and Mycosphaerella (Corlett 1981; Peever et al. 2007; Tibpromma et al. 2017). The holotype (WSP 71448) and isotype (BPI 878440, K 157110) materials of A. pisi are available (Chilvers et al. 2009). The phylogeny based on a combined LSU, ITS, RPB2 and TUB2 sequence dataset confirmed that our strain is sister to the strain CBS 122750 and clusters with other representative strains (CBS 122751, CBS 126.54, CBS 108.49) and the ex-type strain of A. pisi (CBS 122785). These isolates were collected from Pisum sativum in different localities, except the strain CBS 108.49 which was isolated from Juglans regia in Netherlands. Our isolate shares similar morphological characters to the type of A. pisi (Chen et al. 2015). Both isolates are characterised by scattered groups or individually scattered ascomata, 8-spored, cylindrical asci and hyaline, fusiform, 1-septate ascospores. However, the ascospores of our new collection are longer and slightly wider than the type (HMAS 246705) (Chen et al. 2015). This could be due to environmental factors. In addition, the hamathecium of our collection comprises numerous filamentous, septate, pseudoparaphyses, ostiole is conspicuous with a long neck and asci show a deep ocular chamber, while in HMAS 246705, the hamathecial elements are lacking, the ostiole is inconspicuous and the ocular chamber in the asci is shallow (Chen et al. 2015). As per the guidelines of Jeewon and Hyde (2016) we have analysed nucleotide differences within the rRNA gene region for further clarification. In comparison of ITS regions (ITS1-5.8S-ITS2) from 422 nucleotides there is 1 bp (0.23%) difference between MFLUCC 18-1351 and CBS 122750 strains. LSU rDNA region has 2 bp (0.24%) differences from 832 bp. In considering morpho-molecular data analysis, we conclude that our new collection is another record of Ascochyta pisi and also a new host record on Dioscorea communis (Dioscoreaceae) in Italy.