Conidiobolus srinivasanii K.S. Pawar, P.N. Singh, S.K. Singh, 2025

Conidiobolus srinivasanii K.S. Pawar, P.N. Singh, S.K. Singh sp. nov. ( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Mycobank MB856744

Etymology:— Named after M.C. Srinivasan, Indian mycologist, to honour his immense contribution in the field of mycology.

Description:— Asexual morph. Hyphae branched, aseptate when young, septate and vacuolated upon maturation, smooth-walled, pigmented, 4.8–13.8 μm wide. Primary conidiophores often arising laterally from superficial hyphae, unbranched, smooth-walled, hyaline, 52–360 μm long, vasiform, swollen at middle, 6.6–28 μm wide, base slightly narrow, septate, septa thickened and darkened, bearing single primary conidia, vacuolated upon discharge of conidia. Primary conidia globose to subglobose, papillate, catenate, forcibly discharged, smooth-walled, hyaline, germination mono- to multipolar, 23.8–59 × 17.7–52.6 μm. Papilla conical, 7.9–15.2 μm long and 7.3–12μm wide. Secondary conidia, smooth-walled, catenate, with 2 to 4 replicative conidia, produced on short secondary conidiophores developing from primary conidia, smaller than primary conidia, terminal conidia pigmented, dark brown, forcibly discharged upon maturation. Microconidia rarely observed, ellipsoidal, narrowly papillate, smooth-walled, base narrowly truncate, hilum unthickened, hyaline, 10.4–17.8 × 7.2–13 μm, arising from 9.7–14 μm long and 4–5.3 μm wide stalk produced from primary conidia, forming coronoid structure with 7 to 18 microconidia. Villose conidia globose to subglobose, formed after 7 to 8 days, 31.4–41.6 × 27–39.6 μm. Sexual morph. Zygospores, intercalary, globose to subglobose, smooth-walled, hyaline, produced from the conjugation of adjacent segment of hyphae after 8 to 10 days, 28.5–48.6 μm diam., with 1–3 μm thick wall.

Culture characteristics:— On potato dextrose agar, at 25 °C after 7 days of incubation, colony reaching 27 mm diameter, forcibly discharged conidia around the colony covering the circular area with diameter up to 90 mm, flat, powdery, 1A2 (yellowish white), reverse 2A3 (pale yellow), margin irregular. Colour code follows Methuen Handbook of Colour ( Kornerup & Wanscher 1978).

Material examined:— INDIA. Maharashtra: Pune, Vetal Hill, from plant litter, 1 Oct 2020, K.S. Pawar, AMH 10777 (holotype), deposited in Ajarekar Mycological Herbarium ( AMH), India. NFCCI 5839 (ex-type culture) deposited in the National Fungal Culture Collection of India ( WDCM 932).

GenBank numbers:— nucLSU = PQ536954, TEF-1α = PQ541123, mtSSU = PQ536953.

Notes:— Conidioolus srinivasanii is grouped with C.coronatus Batko and C.megalotocus Drechsler in phylogenetic tree. However, it presents several morphological features that highlight its distinctiveness and differentiate it from other species of Conidiobolus s.s. The primary conidiophore in C. srinivasanii is vasiform and longer than those of C. coronatus (53–287 μm) and C. megalotocus (20–125 μm). The primary conidia of C. srinivasanii (23.83–59.10 × 17.69–52.60 μm) differ from the smaller conidia of C. coronatus (17–48.5 × 14.5–38.5 μm) and C. megalotocus (12–44 × 10–42 μm) ( Batko 1964, Drechsler 1956). Conidia of C. megalotocus lack the distinct multipolar germ tube formation and pigmentation observed in C. srinivasanii . Additionally, C. srinivasanii is distinguished by its unique catenate secondary conidia, forming chains of 2 to 4 conidia, a feature which is absent in other Conidiobolus s.s. species.

Phylogenetic analysis

The multi-gene phylogenetic analysis performed using IQ-TREE was based on an alignment of 26 sequences. The three loci concatenated sequence contained 2053 characters of TEF-1α (1–500), mtSSU (501–987) and nucLSU (988– 2060). Among the 2060 positions, 866 were distinct patterns, 457 were parsimony-informative sites that provided the critical information for distinguishing between different evolutionary histories. Additionally, there were 1213 constant sites, identical across all sequences in the alignment, and 390 singletons. The best-fit model for the dataset, determined using the Bayesian information criterion ( BIC), was GTR+F+I+G4, with model parameters optimized to final loglikelihood of -12345.225. Base frequencies showed adenine (A) was the most prevalent at 32.5%, followed by thymine ( T) at 27.8%, guanine (G) at 22.8%, and cytosine (C) at 16.9%. Additionally, gamma shape parameter (α) of 0.416 highlighted considerable rate variations among sites, reflecting a wide range of evolutionary rates. To assess reliability of the inferred phylogenetic tree, the analysis included ultrafast bootstrap (1000 replicates) for branch support. The bootstrap correlation coefficient was found to be 0.995, suggesting a high consistency in the support values across replicates. The final tree, supported by robust statistical analyses, provides a well-resolved phylogenetic hypothesis for the sequences of C. srinivasanii NFCCI 5839 ( Fig. 3 View FIGURE 3 ). In line with previous studies ( Nie et al. 2020 a, b, Gryganskyi et al. 2022), the current phylogenetic tree clearly demonstrates the grouping of all Conidiobolus s.s. members into two distinct main clades, highlighting the robustness and consistency of the phylogenetic structure observed across multiple analyses.