Fungalpedia – Note 130 Boeremia
Boeremia Aveskamp, Gruyter & Verkley
Citation when using this entry: Aumentado et al. in prep – Fungalpedia, plant pathogens. Mycosphere.
Ascomycota, Pezizomycotina, Dothideomycetes, Pleosporomycetidae, Pleosporales, Didymellaceae
Boeremia was introduced by Aveskamp et al. (2010) to accommodate phoma-like species that share morphological similarities with Phoma exigua. This genus is typically characterized by variable-shaped and sized pycnidial conidiomata, mostly globose to subglobose, smooth or with few mycelial outgrowths on the agar surface or immersed. These pycnidia can be solitary or confluent, with 1–2(–3) ostioles that are apapillate or papillate. When mature, the ostioles are internally lined with papillate hyaline cells. The pycnidial wall consists of pseudoparenchymatous tissue, composed of 2–8 cell layers, with the outer 1–3 layers being brown pigmented. The conidiogenous cells are phialidic, hyaline, simple, smooth, ampulliform to doliiform. The conidia vary in shape and are hyaline, thin-walled, smooth, and mainly aseptate, but occasionally 1(–2)-septate conidia may be found. Pseudothecia are only rarely observed in one species in vivo, and they are subglobose. The asci are cylindrical or subclavate, always 8-spored and biseriate whereas ascospores are ellipsoid and uniseptate (Jayawardena et al. 2019, Jayasiri et al. 2017, Aveskamp et al. 2010, Boerema 2004).
This genus is accepted in Didymellaceae (Hongsanan et al. 2020, Wijayawardene et al. 2022). Boeremia can be distinguished from other genera in Didymellaceae based on the morphology of its ostiole. Its ostioles have a smooth lining and distinct hyaline cells surrounding the ostiolar openings. Moreover, these species produce fewer conidia in culture compared to the host (Aveskamp et al. 2010). There are 22 species associated with Boeremia, identified through a combination of morpho-molecular sequence data of recommended genetic markers, internal transcribed spacer (ITS) region, 28S ribosomal RNA gene (LSU), RNA polymerase II second largest subunit (RPB2), β-tubulin (β-tub), and translation elongation factor 1-alpha (tef1-α) (Jayawardena et al. 2019, Jayasiri et al. 2017, Marin-Felix et al. 2017, Chen et al. 2015, 2017, Aveskamp et al. 2010, Berner et al. 2015).
Boeremia is a ubiquitous necrotrophic plant pathogen that can affect all foliar parts of a plant (Berner et al. 2015, You et al. 2016, Zhao et al. 2016, Gai et al. 2016, Grinbergs et al. 2014, 2016). It causes dark brown sunken lesions at the base of the plant, which eventually expand to girdle the stem, resulting in yellowing and wilting of older leaves, ultimately leading to the death of the plant. In the case of fruit infection, it begins as water-soaked lesions that rapidly progress into sunken brown/black/gray lesions with concentric rings. Leaf lesions, on the other hand, start as small spots and develop into brown/ gray lesions with concentric rings (Zhao et al. 2016, Jones et al. 2011). Pathogenicity studies have been conducted on Abelmoschus esculentus (Zhao et al. 2016), Coffea arabica (Núñez et al. 2011), Rhaponticum repens (Berner et al. 2015), Phaseolus spp. (Gorny et al. 2015, Ríos et al. 2014, Li et al. 2012), and Pyrethrum sp. (Zhao et al. 2016) to confirm its pathogenicity on the respective hosts. A study by Berner et al. (2015) on host range, disease incidence, and severity of B. rhapontica demonstrated that its capacity to infect is confined to a very specific range of hosts within the Rhaponticum group. In contrast, other weed species that were examined displayed a maximum severity of 20% (Berner et al. 2015, Hidalgo et al. 2006). Whereas B. exigua has been documented causing leaf spot Panax japonicus infecting around 95% of plants in the field and resulting in substantial necrotic lesions on the leaves with elliptical and irregularly shaped margins at the leaf tip (You et al. 2016). Another study of B. exigua on Cichorium intybus induced dark, firm, sunken lesions on the root. As the disease progresses, these lesions transform into cavities that are black on the crown of the plant resulting in yield reductions of up to 31% (Grinbergs et al. 2014, 2016). Boeremia also can be found as saprobes on various plant species including Chamaedaphne calyculata, Cheiranthus cheiri, Crinum powellii, Cynara scolymus, Dactylis purpurea, Dahlia sp., Digitalis sp., Foeniculum vulgare, Forsythia sp., Fraxinus excelsior, Hedera helix, Hydrangea paniculata, Galium sp., Ipomoea batatas, Lamium maculatum, Lathyrus sp., Leonurus cardiaca, Linum usitatissimum, Lonicera sp., Lycopersicon esculentum, Malus domestica, Melissa officinalis, Mentha sp., Nemophila insignis, Nerium oleander, Nicotiana tabacum, Origanum dubium, Oxycoccus macrocarpus, Philadelphus sp., Phlox sp., Pisum sativum, Populus euramericana, Salix sp., Sambucus nigra, Sedum spp., Solanum tuberosum, Syringa vulgaris, Tanacetum cinerariifolium, Trachelospermum jasminoides, Ulmus sp., Veronica officinalis, Viburnum opulus, and Vitis sp. (Farr & Rossman 2023).
Type species: Boeremia exigua (Desm.) Aveskamp, Gruyter & Verkley
For other species: Species Fungorum, search Boeremia for names
Herbert Dustin R. Aumentado, Center of Excellence in Fungal Research and School of Science, Mae Fah Luang University, Chiang Rai, Thailand
Edited by Ruvishika S. Jayawardena & Kevin D. Hyde