Allophoma

Fungalpedia – Note 126 Allophoma

Allophoma Qian Chen & L. Cai

Citation when using this entry: Aumentado et al. in prep – Fungalpedia, plant pathogens. Mycosphere.

Index Fungorum, Facesoffungi, MycoBank, GenBank

Ascomycota, Pezizomycotina, Dothideomycetes, Pleosporomycetidae, Pleosporales, Didymellaceae

Allophoma was recognized by Chen et al. (2015) with A. tropica as the type species based on morphological characteristics and phylogenetic studies. Allophoma was introduced to encompass a novel species and five species previously included in Phoma with various shaped conidia (Chen et al. 2015). There are 14 established species identified through morpho-molecular data analysis employing genetic markers such as the internal transcribed spacer (ITS) region and the 28S large ribosomal subunit RNA (LSU) gene and protein-coding genes: beta-tubulin (β-tub), and RNA polymerase II second largest subunit (rpb2) gene regions (Chen et al. 2015, 2017, Valenzuela-Lopez et al. 2018, Babaahmadi et al. 2018, Marin-Felix et al. 2019, Jayasiri et al. 2019, Huo et al. 2020, Yuan et al. 2021).

Allophoma is characterized by its ovoid, oblong, aseptate conidia which can be ellipsoidal to cylindrical, or somewhat allantoid (Chen et al. 2015). The conidiomata are pycnidial and can be globose to flask-shaped. Conidiomata are found either on the surface of agar or submerged in it. The pycnidial wall consists of pseudoparenchymatous tissue, typically composed of 2 to 5 cell layers. The conidiogenous cells are phialidic, hyaline, and smooth. Conidiogenous cells are ampulliform, doliiform, flask-shaped, or isodiametric. The conidia are hyaline, thin-walled, smooth, and aseptate. These conidia vary in both shape and size as some are ovoid, oblong, ellipsoidal to cylindrical, or somewhat allantoid, and often contain guttules (Chen et al. 2015, 2017).

Several species of Allophoma are important phytopathogens, causing various plant diseases such as leaf spot, necrosis, canker, seed rot, and dieback to various plant species. i.e., Lantana camara, Lactuca sativa, Euphorbia milii, Solanum lycopersicum, Citrullus colocynthis, Cucurbita pepo, and Syzygium cumini (Farr & Rossman, 2023). Disease symptoms include leaf lesions that are dispersed, irregularly shaped, and clearly defined and can be found both on the upper surface and underside of the leaf (Yuan et al. 2021). On the stem, it appears as spots that can rapidly develop to a soft, black cortical rot whereas portions of the stem that did not exhibit any symptoms remained intact without any signs of decay (O’Neill & Mayne 2016). Pathogenic species of Allophoma include A. zantedeschiae (Boerema 1993), A. piperis (Boerema et al. 2004), A. labilis (O’Neill & Mayne 2016, Nagarjun & Suryanarayana 2016, Keshavarzi et al. 2023, Demir et al. 2023), A. tropica (Schneider & Boerema 1975, Boerema et al. 2004, Zimowska 2011, Gilardi et al. 2018) and A. hayatii (Babaahmadi et al. 2018). Whereas the recently introduced species A. thunbergiae causes leaf spots of Thunbergia grandiflora (Yuan et al. 2021). Pathogenicity studies have been conducted on Syzygium cumini (Nagarjun & Suryanarayana 2016), Solanum lycopersicum resulting in stem girdling (O’Neill & Mayne 2016), Cucurubita pepo seeds inciting seedling root and crown rot (Demir et al. 2023), and Lantana camara stems causing external longitudinal necrosis in the bark, and cracking of the stem cortex (Babaahmadi et al. 2018).