Multigene phylogeny and morphology reveal Cytospora spiraeae sp. nov. (Diaporthales, Ascomycota) in China

Abstract

Members of Cytospora encompass important plant-associated pathogens, endophytes and saprobes, commonly isolated from a wide range of hosts with a worldwide distribution. Two specimens were collected associated with symptomatic canker and dieback disease of Spiraea salicifolia in Gansu, China. These isolates are characterized by its hyaline, biseriate, aseptate, elongate-allantoid ascospores and allantoid conidia. Cytospora spiraeae sp. nov. is introduced based on its holomorphic morphology plus support from phylogenetic analysis (ITS, LSU, ACT and RPB2), and differs from similar species in its host association.

Discovery of Cytospora species associated with canker disease of tree hosts from Mount Dongling of China

“…Morphologically, it differs from C. spiraeae by the smaller perithecia (210-250 vs. 270-400 µm in diam.) and longer ascospores (8.5-12 × 2.5-3.5 vs. 7-8 × 2-2.5 µm) (Zhu et al 2018a). Phylogenetically, C. spiraeicola (CFCC 53138) differs from C. elaeagnicola (CFCC 52882) by ITS (8/665), rpb2 (44/730), tef1-α (75/771) and tub2 (42/624) and C. spiraeae (CFCC 50049) by ITS (4/665), rpb2 (38/730), tef1-α (63/771) and tub2 (44/624) (Zhu et al 2018a, Zhang et al 2019.…”

“…Ambiguously aligned sequences were excluded from analysis. Reference sequences were selected, based on ex-type or ex-epitype sequences available from recently published literature (Fan et al 2014a, b, 2015a, b, 2020, Yang et al 2015, Lawrence et al 2016, Norphanphoun et al 2017, Zhu et al 2018a, Zhang et al 2019 A partition homogeneity test (PHT) with heuristic search and 1,000 replicates was performed using PAUP v.4.0b10 to test the discrepancy amongst the ITS, LSU, act, rpb2, tef1-α and tub2 sequence datasets in reconstructing phylogenetic trees. MP analysis was performed using a heuristic search option of 1,000 random-addition sequences with a tree bisection and reconnection (TBR) branch swapping algorithm (Swofford 2003).…”

“…Other parsimony scores, such as tree length (TL), consistency index (CI), retention index (RI) and rescaled consistency (RC), were calculated (Swofford 2003). ML analysis was performed with the GTR + G + I model of site substitution following recent studies (Zhu et al 2018a), including estimation of gamma-distributed rate heterogeneity and a proportion of invariant sites using PhyML v. 3.0 (Guindon et al 2010). The branch support was evaluated with a bootstrapping method of 1,000 replicates (Hillis and Bull 1993).…”

“…It is characterised by single or labyrinthine of pycnidial locules, filamentous conidiophores (enteroblastic and phialidic conidiogenous cells) producing hyaline, allantoid conidia in the asexual morph; diaporthalean-like perithecia, clavate to elongate obovoid asci with four or eight hyaline, allantoid ascospores in the sexual morph (Spielman 1983, 1985, Adams et al 2005. Species of Cytospora contain important pathogens that cause stem canker and dieback disease on more than 100 species of woody and coniferous plants, thereby causing severe commercial and ecological damage and significant losses worldwide (Sinclair et al 1987, Adams et al 2005, 2006, Fan et al 2014a, b, 2015a, b, Lawrence et al 2018, Pan et al 2018, Zhu et al 2018a, Zhang et al 2019. Previous Cytospora species and their related sexual morphs viz.…”

“…Species identification criteria of Cytospora were previously carried out by the hostbased method and morphology in China; however, these bases are unreliable due to the uninformative illustrations and descriptions, weak host specificity and overlapping morphological characteristics (Teng 1963, Tai 1979, Wei 1979). Recent studies have been able to use multiphase approaches to solve the taxonomy of Cytospora (Fan et al 2014a, b, 2015a, b, Yang et al 2015, Lawrence et al 2016, Norphanphoun et al 2017, Pan et al 2018, Zhu et al 2018a, Zhang et al 2019. Fan et al (2020) summarised 52 species of Cytospora associated with canker and dieback disease in China, using a six gene matrix (ITS,LSU,act,rpb2,, of which 13 species were newly introduced.…”