Xenosphaeropsis pyriputrescens (C.L. Xiao & J.D. Rogers) F. Liu, Crous & L. Cai, comb. nov.
MycoBank number: MB 840273; Index Fungorum number: IF 840273; Facesoffungi number: FoF12732; Fig. 50, 51
Basionym. Sphaeropsis pyriputrescens C.L. Xiao & J.D. Rogers, Pl. Dis.88: 116. 2004.
Typus. USA, Washington State, Wenatchee, Chelan County, on fruit of d’Anjou pear (Pyrus communis), 19 Mar. 2002, C.L. Xiao, holotype of Sphaeropsis pyriputrescens WSP 70466, isotype WSP 70467.
Symptoms — Xenosphaeropsis pyriputrescens causes stem-end rot, calyx- end rot and wound-associated rot on fruit. The decayed tissue is initially ﬁrm or spongy, brown. Subsequently, as the disease advances, the decayed areas remain brown or turn dark brown to dark due to the black pycnidia produced by the fungus. Decay in the fruit flesh originates from infection of the stem or calyx and then develops along the vascular tissue, brown (Xiao & Rogers 2004).
Conidiomata pycnidial, sub-immersed or immersed, subglobose, separate to aggregate in small numbers, off-white to salmon, covered by white aerial mycelia. Conidiophores hyaline, rarely pale brown, constricted at the septum, often reduced to conidio- genous cells. Conidiogenous cells subcylindrical to cylindrical, obclavate, 7.5 – 25(– 37) × 3 –7 μm, lining wall of pycnidium, hyaline, rarely pale brown. Conidia hyaline when immature, be- coming brown with time, aseptate, clavate, ovoid, subglobose, or occasionally ellipsoidal, smooth, 10 –19.5 × 7.5 –13.5 μm (av. ± S.D. = 14.6 ± 2.4 × 10.9 ± 1.8 μm).
Additional material examined. USA, Washington State, Peshastin, Chelan County, dried culture isolated from a decayed fruit of d’Anjou pear (P. com munis) collected from a commercial fruit packinghouse, 12 Dec. 2001, C.L. Xiao, WSP 70468, living culture CBS 115176 = ATCC MYA-2947.
Habitat — Malus domestica, M. sylvestris, Pyrus communis.
Geographic distribution — AMERICA: Canada, USA.
NCBI Genome ID: JAGKQE000000000 (CBS 115176, this study).
Notes — Although the holotype (WSP 70466) and isotype (WSP 70467) of Sphaeropsis pyriputrescens were designated in Xiao & Rogers (2004), their corresponding cultures and se- quences were not mentioned, and could not be located. There- fore, the living culture ATCC MYA-2947 listed as representative in Xiao & Rogers (2004) was examined and sequenced in this study.
Sphaeropsis was clariﬁed as the asexual morph of Phaeobo tryosphaeria, taxonomically belonging to Botryosphaeriaceae (Botryosphaeriales) (Phillips et al. 2008, Zhang et al. 2021). However, multi-locus (LSU, ITS, rpb2) phylogenetic analysis allocated the ex-paratype of S. pyriputrescens (CBS 115176) in the clade of Phacidiaceae (Phacidiales) (Fig. 51). It clustered together with three reference strains from pear and apple, and showed certain morphological differences and phylogenetic distance from other genera in Phacidiaceae. A novel mono- typic genus, Xenosphaeropsis, was therefore introduced to accommodate this species. Xenosphaeropsis pyriputrescens is currently limited on Pyrus communis in Washington and British Columbia (Xiao & Rogers 2004, Sholberg et al. 2009) and on Malus sp. in Washington and New York (Xiao & Rogers 2004, Xiao & Boal 2005, Kim & Xiao 2008, Kim et al. 2013, 2014, Xiao et al. 2014).
Fig. 50 Xenosphaeropsis pyriputrescens (CBS 115176). a. Colony on PDA (20 °C); b. green aerial mycelia producing on the surface of medium with time;
c. pycnidia covered with white aerial mycelia; d– l. conidiogenous cells bearing immature conidia; m– s. mature conidia. — Scale bars: d– m = 10 μm, m ap- plies to n– s.
Fig. 51 Phylogenetic tree of Xenosphaeropsis pyriputrescens calculated with Bayesian analysis on LSU, ITS, and rpb2 sequences showing afﬁnities of X. pyriputrescens with allied species. Thickened branches indicate branches present bootstrap support values (> 50 %) in the RAxML tree. The posterior prob- abilities > 0.90 are displayed at the nodes. Asterisk (*) indicate ex-type culture.