Dothiorella franceschinii Linaldeddu, A. Alves & A.J.L. Phillips, sp. nov.
Index Fungorum number: IF 901118; MycoBank number: MB 901118; Facesoffungi number: FoF 13942; Fig. 1
Etymology – in honour of Professor Antonio Franceschini for his outstanding work on Mediterranean maquis diseases.
Saprobic or weak pathogen on Rhamnus alaternus L. Sexual morph: Undetermined. Asexual morph: Conidiomata pycnidial, produced on R. alaternus twigs on ½ PDA within 2–3 weeks, solitary or aggregated, dark-brown to black, globose, unilocular or multilocular. Conidiomatal wall thick, inner layer comprises thin-walled, hyaline cells of textura angularis, and outer layer comprises dark brown, thin-walled cells of textura angularis. Conidiophores reduce to conidiogenous cells. Conidiogenous cells 6–13×3–7 μm, holoblastic, discrete, cylindrical, hyaline, smooth, indeterminate, proliferating percurrently to form annellides. Conidia 18–27 × 7–10 μm (x=22.8±2.4 × 8.8±0.8 µm, l/w ratio=2.6±0.2, n=50) ellipsoid to ovoid, moderately thick-walled, smooth to finely verruculose inner surface, ends rounded, sometimes with a truncate base, occasionally constricted at septum, initially hyaline and aseptate, becoming pale brown and 1-septate while attached to the conidiogenous cells, with 2 equal or sometimes asymmetric cells, finally dark brown. Microconidia not observed.
Culture characteristics – Colonies on PDA reached 90 mm diam. in 7 days at 22 °C in the dark. Irregular, flat, wavy margin, zonation with maturity, less areal mycelia, initially surface white, turned pale green to dark olivaceous; reserve colony black in middle and dark grey at the edge. Cardinal temperature for growth: minimum<5 °C, maximum 33 °C and optimum 22 °C. Isolates failed to grow at 35 °C but mycelium resumed growth when plates were moved to 22 °C.
Material examined – Italy, Caprera Island, from sunken canker on stems of Rhamnus alaternus (Rhamnaceae), 3 May 2012, B.T. Linaldeddu, (CBS H-24771, holotype, a dried culture sporulating on Rhamnus alaternus twigs), exholotype culture BL151=CBS 147722.
GenBank numbers – ITS: OP999677, tef1-α: OQ067247.
Notes – Our collection (CBS-H 24771) phylogenetically closed to Dothiorella eriobotryae and D. prunicola, however form a distinct sister clade to Dothiorella eriobotryae with ML=100% statistical values (Fig. 2). Our collection shows 0.21% and 4.39% base-pair differences in the ITS and tef1-α loci of D. eriobotryae respectively. The basepair differences in the ITS and tef1-α loci of D. prunicola with our strain revealed 1.89% and 13.18% respectively. Furthermore, our collection differs from D. eriobotryae (average size of conidia 19.7 × 10.3 μm, l/w ratio = 1.9) on account of its longer and narrower conidia and from D. prunicola (average conidia size 24.5 × 12.8 μm, l/w ratio=1.9) on account of its shorter and narrower conidia. Therefore, we introduce our collection as Dothiorella franceschinii sp. nov.
Figure 1 – Dothiorella franceschinii (CBS 147722, ex-holotype). a Surface view of colony on PDA. b Horizontal cross section of pycnidia formed on Rhamnus alaternus twigs. c–d Immature conidia developing on conidiogenous cells. e Mature conidia attached to the percurrently proliferating conidiogenous cell (arrowed). f Mature conidia constricted at the septum with asymmetric cells. Scale bars: c–f=20 μm
Figure 2 – Phylogram generated from maximum likelihood analysis based on combined ITS and tef1-α sequence dataset. Sixty-three Dothiorella strains were included in the combined sequence analysis, which comprise 732 characters. Neofusicoccum luteum (CBS 562.92) and N. parvum (CMW9081) were used as the outgroup taxa. The tree with the highest log likelihood (− 4506.99) is shown. A discrete Gamma distribution was used to model evolutionary rate differences among sites (5 categories (+G, parameter=0.2070)). The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Bootstrap support equal or greater than 50% are given at the nodes. Ex-type strains are in bold and newly generated sequences are indicated in blue bold