onestopshopfungi - Chaetothyrina

Chaetothyrina Theiss., Annls mycol. 11(6):495 (1913)

The genus Chaetothyrina was established by Theissen (1913), with C. musarum (Speg.) Theiss. as the type species. Chaetothyrina was placed in Micropeltidaceae based on its superficial, flattened base, poorly developed thyriothecium and irregular meandering arrangement of compact hyphae of walled cells. Singtripop et al. (2016) provided molecular data of one reference specimen and one new species. Hongsanan et al. (2017) established a new species of Chaetothyrina and introduced a new family Phaeothecoidiellaceae to accommodate species of Chaetothyrina, Houjia, and Phaeothecoidiella in Capnodiales. Based on its placement in phylogenetic trees and the morphological uniqueness, Micropeltidaceae was excluded from Microthyriales and treated as family incertae sedis in Lecanoromycetes (Hongsanan et al. 2017; Zeng et al. 2019).

Classification – Dothideomycetes, incertae sedis, Capnodiales, Phaeothecoidiellaceae

Type species – Chaetothyrina musarum (Speg.) Theiss., Annls mycol. 11(6):495 (1913)

Distribution – Known from Brazil, Cook Islands, Dominican Republic, India, Mexico, Pakistan, Panama, Thailand, US

Disease symptoms – Sooty blotch and flyspeck

Species in this genus cause flyspeck disease on various plants, such as C. musarum on Musa sp. and C. panamensis (F. Stevens & Dorman) Arx on Oncoba laurina. Sooty blotch and flyspeck (SBFS) is a disease complex caused by nearly 80 fungal species (Singtripop et al. 2016) that are epiphytes which blemish the epicuticular wax layer of several fruit crops, such as apple, pear, orange, persimmon, banana and grape worldwide (Gleason et al. 2011; Gao et al. 2014), cutting sale price and limiting the growth rate of fruit production (Williamson et al. 2000; Gao et al. 2014). ‘Sooty blotch’ is characterized by colonies produced on host tissues from superficial, spreading, dark irregular blotches of mycelium with or without sclerotium-like structures or fruiting bodies. On the other hand, ‘flyspeck’ defines clusters of shiny, small, black sclerotium-like structures or fruiting bodies, lacking visible intercalary mycelium (Gleason et al. 2011; Mayfield et al. 2013; Singtripop et al. 2016).

Hosts – Species of Anacardium, Anodendron, Anogeissus, Carallia, Cassia, Chonemorpha, Dalbergia, Dianella, Euonymus, Hevea, Iiana, Magnifera, Magnolia, Mammea, Maytenus, Memecylon, Mitragyna, Musa, Myrcia, Ochrocarpos, Olea, Oncoba, Phoebe, Similax, Streblus and Vochysia.

Fig. Disease symptoms caused by Chaetothyrina spp. a on mango. b, d appearance of thyriothecia on hosts. c on a banana. e on mango leaves.

Morphological based identification and diversity

Chaetothyrina is characterized by superficial, flattened thyriothecia, with base poorly developed, with thyriothecial setae and 1-septate ascospores (Reynolds and Gilbert 2005; Singtripop et al. 2016; Hongsanan et al. 2017). Chaetothyrina can be distinguished from other species in Micropeltidaceae on the basis of thyriothecial setae appearance, shape, and septation of the ascospores (Singtripop et al. 2016; Hongsanan et al. 2017). Twenty-three species of Chaetothyrina epithets are listed in Index Fungorum (2019), but sequence data are available for only two species (4/7/2019). Chaetothyrina is a poorly studied genus. Fresh collections and sequence data are needed for this genus. The disease cycle of this genus is yet to be established.

Fig. Chaetothyrina guttulata a Thyriothecium when viewed in squash mount. b Surface of thyriothecium. c Section through thyriothecium. d Ascus when immature. e Asci at maturity. f Ascospores. Scale bars: a=50 µm, b, d, e=10 µm, c=100 µm, f=5 µm.

Molecular based identification and diversity

Singtripop et al. (2016) provided a reference type specimen of C. musarum with sequence data. Using combined LSU, SSU and ITS sequence data, Chaetothyrina clustered as a sister genus to Houjia and Phaeothecoidiella within Capnodiales (Hongsanan et al. 2017; Fig. 6).

Recommended genetic markers (genus level) – LSU and SSU

Recommended genetic markers (species level) – ITS and RPB2

The accepted number of species: There are 23 epithets in Index Fungorum (2019). However, only two species have molecular data.

References: Reynolds and Gilbert 2005; Singtripop et al. 2016; Hongsanan et al. 2017 (morphology, phylogeny)

Fig. Phylogenetic tree generated by maximum parsimony analysis of combined LSU, SSU and ITS sequence data. Thirty-nine strains are included in the analyses, which comprised 2225 characters including gaps. The tree was rooted with Myriangium duriaei (CBS 260.36) and M. hispanicum (CBS 247.33). The maximum parsimonious dataset consisted of 1645 constant, 461 parsimony-informative and 119 parsimony-uninformative characters. The parsimony analysis of the data matrix resulted in the maximum of ten equally most parsimonious trees with a length of 1637 steps (CI = 0.549, RI 0.736, RC = 0.404, HI = 0.451) in the first tree. MP and ML bootstrap values ≥50% and Bayesian posterior probabilities ≥0.90 (BYPP) are shown respectively near the nodes. Ex-type strains are in bold.

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