Backusella solicola V.G Hurdeal & E. Gentekaki, 2022

Hurdeal, Vedprakash G., Gareth Jones, E. B., Santiago, André Luiz C. M. De A., Hyde, Kevin D. & Gentekaki, Eleni, 2022, Expanding the diversity of mucoralean fungi from northern Thailand: novel Backusella species from soil, Phytotaxa 559 (3), pp. 275-284 : 280

Backusella solicola V.G Hurdeal & E. Gentekaki , sp. nov. FIGURES 1 and 2

MycoBank: MB844700

Typification: THAILAND, Chiang Rai province, Mae Suai district , elevation 1052 m, 19°47’19.9”N, 99°33’23.3”E, July 2021, soil from a coffee farm, collected by Eleni Gentekaki and isolated by Vedprakash G. Hurdeal (Holotype MFLU 22-0123 ; ex-type living culture MFLUCC 22-0067 ). GenBank: 28S = ON892503 ; ITS = ON899832 .

Diagnosis: The protologue of B. gigacellularis ( de Souza et al. 2014) described this species with larger sporangia (40–131 μm vs 35.5–71.5 µm diam) and sporangiospores (9–39×5.5–19.5 μm vs 11–14.5×8–10.5 µm) than B. solicola . Furthermore, B. solicola produces unispored sporangiola (rare), as opposed to its sister taxa, whereby this character was not observed in B. gigacellularis culture. Backusella solicola also produces larger multispored sporangiola (22.5– 31.5 × 22.5–35 µm vs 23 μm) and slightly larger columellae (27.5–54.5 × 22–35 µm vs 9.4–53×8.2–46 μm) than B. gigacellularis . The sexual stages of B. solicola to B. gigacellularis were not compared as in both species this stage was not observed. Molecular phylogeny also supported these morphological differences. In all phylogenetic analyses, B. solicola and B. gigacellularis were segregated with high statistical support. The genetic distance in the ITS regions of these two taxa is around 15 %, and gives more resolution to the species delimitation.

Etymology: epithet refers to the source from which the fungus was isolated.

Description: Asexual morph on MEA at 25 °C for 3-5 days. Substrate mycelia contain inflated regions with brown droplets ending with rhizoid-like filaments. Sporangiophores hyaline to pale brown, variable in length, undulate, transitorily curved when young and erect at maturity, 4.5–17 µm wide (x = 11.5 µm, n = 40), simple or sympodially branched, with a septum occasionally observed below the sporangium. Sporangiophores frequently broader at the base and then tapering slightly near the base of the sporangium. Sporangia pale brown to brown, globose, 34.5–67.5× 35.5–71.5 µm (x = 47.5× 48.5 µm, n = 30), minutely spinulose. Columellae hyaline, subglobose, ellipsoidal, oblong to cylindrical (often constricted in the centre), pyriform, conical, non-collapsing, 27.5–54.5 × 22–35 µm (x = 41.5 × 30.5 µm, n = 30), smooth-walled; collar short ( FIG. 2 L–Q ). Sporangiola multispored, rarely unispored, pale brown to brown, globose to subglobose, often produced in short sympodially branched sporophores, 22.5–31.5 × 22.5–35 µm (x = 25 × 26µm, n = 30), containing 4–8 sporangiospores each; wall persistent and spinulose ( FIG. 2I, J ). Columellae of sporangiola hyaline, smooth-walled subglobose or conical. Sporangiospores hyaline to pale, brown ellipsoidal and few irregularly shaped, 11–14.5× 8–10.5 µm (x = 12.5× 9.5 µm, n = 40). Chlamydospores and rhizoids present. Sexual morph was not observed.

Culture characteristics as observed in MEA and PDA: In MEA, initially (day 1-24 hours post-inoculation), at 15-28 °C, the colony morphology is flat, moist and yeast-like with only few strands of hyphae observed. On day 2, the morphology remains the same at 15-25 °C. After day 3 at 28 °C, the colony is white and fluffy with both horizontal and lateral growth. At 25 °C, the colony front is white and the reverse white to pale yellow. Initially (day 1-2), mostly single branches were observed (tall sporangiophores with terminal sporangium), but with maturity sympodial branches were also observed. As the culture matures, sporangiophores with dark brown sporangia and sporangiola are observed. In PDA (in all tested temperatures), colony white with fluffy and cottony appearance with both lateral and horizontal growth. Lateral growth observed from the point of inoculation but absent at the perimeter of the culture. Both simple and sympodially branched sporangiophores were observed. As the colony matures (day 2 onwards), the colony front and reverse remain white with small dark spots (the sporangia) visible with the naked eye. Mostly simple branches of the sporophores observed but sympodial branches were present as well. The sporangiophores were undulate and some erect.

Growth characteristics in MEA: Growth in MEA was slightly faster than in PDA whereby at day 3 the fungus completely covered the inoculated MEA plate in most temperatures (20-28 °C) tested. At day 1, more reproductive structures such as sporangia were observed in MEA than PDA at 20 °C. Growth was observed at temperatures ranging from 15-28 °C. No growth was observed at 4, 8 and 37 °C after 14 days. In all tested temperatures and data obtained from measurements taken after every 24 hours, it was observed that the colony grew faster at 28 °C with better sporulation.

Growth characteristics in PDA: Similar to MEA, growth was fastest at 28 °C. Initially (day 1), at low temperature (15 °C), reproductive structures were rare or not produced yet. As the colony matures, a white colony with simple and sympodially branched sporophores were observed. In other temperatures tested, the colony colour and appearance were similar. At temperatures ranging from 20-28 °C, asexual reproductive structures appear within 24 hours post inoculation. The sporangiophores are simple or sympodially branched. Growth was observed at temperatures ranging from 15-28 °C. No growth was observed at 4 °C, 8 °C and 37 °C after 14 days

Figures

FIGURE 1. Maximum likelihood phylogram inferred from 53 taxa from ITS and 28S genetic markers. Bootstrap support (BS) from RAxML and IQ-tree, and the posterior probability from Bayesian analysis are provided near the nodes as BS/BS (IQ-tree)/ PP. Values <70% for bootstrap support and <0.80 for posterior probability are indicated by a minus sign (–). Unrecovered branching is indicated by (*) sign. The novel strain proposed in the current study is shown in bold. T, ET, LT, and NT indicate ex-type, ex-epitype, ex-lectotype and ex-neotype strains, respectively. Mucor indicus (CBS 226.29) and M. koreanus (EML-QT1) were used as outgroup taxa.

FIGURE 2. Backusella solicola MFLUCC 22-0067 (ex-type). A, B. branching pattern of sporangiophores. C. short branched sporophore with columellae. D, E, H. developmental stages of the sporangium. F. unispored sporangiola. G. sporangiospores. I–J. multispored sporangiolum. K. obverse and reverse of colony in PDA. L–Q. various shaped columellae. Bars: B, C, E, H, J, L–N, P, Q = 20 µm; D, G, O = 10 µm.