Aquastroma magniostiolatum Kaz. Tanaka & K. Hiray. [as ‘magniostiolata‘], in Tanaka et al., Stud. Mycol. 82: 115 (2015)
Index Fungorum number: IF 828557; MycoBank number: MB 828557; Facesoffungi number: FoF 08694, Fig. 1
Saprobic on submerged decaying Sonneratia caseolaris (L.) Engl. stem in a freshwater habitat. Sexual morph: Ascomata 220–260 × 190–250 μm (x = 232 × 228 μm, n = 10), black domes visible on host cortex, solitary to gregarious, immersed to erumpent, subglobose, black, coriaceous, ostiolate, 77–82 μm wide. Peridium 15–27.5 μm (x=21 μm, n=15), thick-walled, thinner at the base, becoming thick at the apex, composed of two layers: outer layer composed of one or two layers of brown thick-walled cells of textura angularis, inner layer composed of hyaline thin-walled cells of textura angularis. Pseudoparaphyses 1.5–3 μm, numerous, cellular, broad, septate, hyaline, smooth-walled, branched and anastomosing above the asci. Asci 60–105 × 15.5–27 μm (x=76.6 × 22.1 μm, n=25), bitunicate, 8-spored, clavate, fissitunicate, apically rounded with invisible apical chamber, sessile or short pedicellate. Ascospores 30–45×4–12 μm (x=38.83×8.53 μm, n=30), bi- to tri-seriate, clavate to fusiform, guttulate to granular, straight, mostly curved, 6–7-septate, constricted at septa, hyaline, smooth-walled, surrounded with mucilaginous sheath. Asexual morph: Undetermined.
Culture characteristics – Conidia germinating on malt extract agar (MEA) within 24 h. Colonies growing on MEA, reaching 25–30 mm in 2 weeks at 25 °C, colony circular, flat, entire, dry, surface rough, smooth hyphae, light brown in surface view, reverse dark gray.
Material examined – Thailand, Samut Songkhram Province, Mueang Samut Songkhram District, on submerged decaying wood of Sonneratia caseolaris (Lythraceae) in a river, 8 September 2020, M. Calabon, SS04 (MFLU 22-0121), living culture, MFLUCC 22-0081.
Hosts and geographical distribution – Dead wood culms of unidentified plant in Japan (Tanaka et al. 2015), and Thailand (Dong et al. 2020), twigs of Sonneratia caseolaris in Thailand.
GenBank numbers – LSU: OP216403, ITS: OP216408, tef1-α: OP251193
Notes – Multi-locus phylogenetic analysis showed that our collection MFLUCC 22-0081 clustered with strains of Aquastroma magniostiolatum with ML/BI=100%/1.00 bootstrap support. The pairwise nucleotide comparisons of our isolate (MFLUCC 22-0081) with the type strain (CBS 139680) showed 0.12%, 1.09% and 0.76% nucleotide differences in the ITS, LSU, and tef1-α regions, respectively. Aquastroma magniostiolatum was isolated in freshwater pond and stream (Tanaka et al. 2015; Dong et al. 2020) and terrestrial habitats (Chethana et al. 2021a). The fungus was reported twice in Thailand from unidentified wood (Dong et al. 2020; Chethana et al. 2021a). Morphological comparisons of our collection (MFLUCC 22-0081) with the freshwater strains CBS 139680 and MFLUCC 18-0976 revealed their similarity. However, our isolate differs from CBS 139680 with a narrower conidiomata (220–260 × 190–250 μm vs. 180–250 × 260–340 μm) and shorter asci (60–105×15.5–27 μm vs. 112.5–137.5×25–29.5 μm). We identified our collection as A. magniostiolatum and this is the first record in decaying twigs of Sonneratia caseolaris (Fig. 2).
Figure 1 – Aquastroma magniostiolatum (MFLU 22-0121). a Riverine mangrove Sonneratia caseolaris. b Examined material. c Appearance of ascomata in host substrate. d Vertical section of ascoma. e Peridium. f Pseudoparaphyses. g–k Asci. l–p Ascospores. [Ascospores stained with Lactophenol Cotton Blue (o) and Indian Ink (p)]. q Germinated ascospore. r Surface view of culture on MEA. s Reverse view of culture on MEA. Scale bars: c=500 µm, d=100 µm, e=20 µm, f=10 µm, g–k=50 µm, l–q=20 µm
Figure 2 – Phylogram generated from maximum likelihood analysis based on combined LSU, ITS, and tef1-α sequence data representing the species of Parabambusicolaceae and related families. Corynespora cassiicola (CBS 100822) and C. smithii (CABI 5649b) were used as the outgroup taxa. Forty-two taxa are included in the combined analyses which comprised 3552 characters (2178 characters for LSU, 474 characters for ITS, 900 characters for tef1-α) after alignment. The best scoring RAxML tree with a final likelihood value of−14,144.062065 is presented here. The matrix had 758 distinct alignment patterns, with 17.47% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.222957, C=0.274911, G=0.283984, T=0.218148; substitution rates: AC=1.015664, AG=2.212569, AT=1.355468, CG=1.027432, CT=5.589665, GT=1.0; gamma distribution shape parameter α=0.210099. Bootstrap support for ML equal to or greater than 75% and BI equal to or greater than 0.95 are given above the nodes. Extype strains are in bold and newly generated sequences are in blue bold