Tremellodendropsidales » Agaricomycetes genera¬†incertae sedis » Dendrosporomyces

Dendrosporomyces prolifer

Dendrosporomyces prolifer Nawawi, J. Webster & R.A. Davey 1977, in Nawawi et al., Transactions of the British Mycological Society, 68(1), 59-63 (1977)

Diagnosis: Mycelium consists of septate, branched, hyaline binucleate hyphae, 2.5-5 µm in width. Conidiophores semimacronematous, mononematous, arising as lateral branches, erect, unbranched, 16-80 µm long x 2-3 µm wide. Conidia holoblastic, terminal, hyaline, branched, consisting of a main axis, mostly hook-shaped, 150-295 µm long, 2.5-3 µm wide at the base, broadening above to 7-8 µm, 8-13 septate and bearing from 7-11 lateral arms arising mostly from the convex side of the axis, up to 250 µm long x 7-8 µm wide. The first 2-3 laterals may in tum give rise to secondary and tertiary branches. On 2% malt extract agar or on potato dextrose agar the colonies attain a diam of 35 rom after 14 days at 25°C. They are colourless, appressed at first, smooth, circular, with a thin advancing margin. As the colony ages, the centre becomes raised slightly, turns creamish, and furrows are formed radially in several places. Sporulation was sparse and scattered on these media. On LCA, a synthetic medium used by Miura & Kudo (1970), the colony attains a diam of 40 mm in 14 days at 25°C. The mycelium remains thin and is composed of inconspicuous hyphae radiating from the point of inoculum and remains colourless with age. Sporulation occurred in scattered patches within 5 days and increased later to cover the entire colony. When mycelial pieces were transferred to shallow water and incubated at 20-25 °C, abundant sporulation occurred within 2 days along the exposed cut edges of the agar and on the water surface. Conidia were also formed embedded in the agar. Fully submerged agar pieces with or without aeration did not sporulate. It appears that the fungus is aero-aquatic. Conidiophores arise laterally from the vegetative mycelium. They are short, erect, semimacronematous, mononematous, 16-80 µm long x 2-3 µm wide, thin-walled, composed of 2-4 cells of which the terminal one is conidiogenous. The clavate terminal portion (Fig. 1A) becomes the usually curves backward slightly, becomes septate, and lateral arms are produced in succession, mostly from the convex side and confined mainly to the lower half of the axis (Figs. 1 B-E, 2-4). These laterals are rarely formed in whorls. The first 3 lateral arms may in turn give rise to secondary branches. Tertiary branches are occasionally formed by the first-formed laterals. Because of their large size and complexly branched conidia, most of them at maturity do not remain erect but fall on their side resting on the agar or on the water surface. When fully grown the conidia are liberated by rupture of the septa between conidia and conidiogenous cells. The mature conidium (Figs. 1 F-G, 5-6) thus consists of a main axis, hook-shaped to variously curved, rarely straight, 150-295 µm long, 8-13 septate, 2.5-3 µm at the base, broadening above to 7-8 µm and remains more or less of uniform width to the rounded apex. Each axis is furnished with 7-11 straight to slightly curved, septate lateral arms. These arms are constricted to 2-2.5 µm and septate at their points of origin, broadening to 7-8.5 µm and tapering only slightly to the rounded apex. The first 2 laterals may grow to the same length as the main axis and bear from 3-6 straight, secondary branches of the same width. These secondary branches also arise in the same one-sided manner and grow up to 140pm long. Tertiary branches may also be produced in some conidia. The number of arms making up a conidium (including the main axis) varies from 12-30. The cells of the conidium are filled with hyaline, foamy protoplasm. It is interesting to note that each cell of the hyphae, conidiophores and conidia is binucleate. When hyphae and conidia are stained with ammoniacal Congo red (1 part 0·88 ammonia: 2 parts distilled water, Congo red 0.005 g/ml), each septum reveals the presence of a conspicuous dolipore, characteristic of a basidiomycete (Figs. 7, 8). The presence of dolipore septa was confirmed by electron microscopy. The fungus was inoculated into 2% liquid malt extract, and incubated for 3 weeks at 20 °C on a Gallenkamp orbital shaker at 150 rev./min. The mycelial mat was cut into small pieces and fixed in 2% aqueous potassium permanganate for 15 min. The mycelial pieces were embedded in Araldite, sectioned, and examined in an AEI 801B electron microscope. As shown in Fig. 9, the septal pore is clearly of the dolipore type, overarched by a parenthesorne. Detached conidia apart from their larger size closely resemble conidia of Dendrospora Ingold, of which two species have been described. In fact, when this fungus was first observed it was tentatively placed in that genus. It resembles D. juncicola Iqbal (1972) in its conidial morphology. In both fungi the conidium is borne at the end of an unbranched conidiophore. The main axis is continuous with the conidiophore and the disposition of the branches is to some extent similar. However, in the type species D. erecta Ingold, the lateral arms arise in pairs or in whorls of three from near the base of the usually straight and uniform main axis. A study of D. erecta shows that the cells are uninucleate and lack dolipore septa as seen in ammoniacal Congo red preparations. According to Ingold (1943) Dendrospora resembles Triscelophorus Ingold, especially during its early stages where the arms are formed in succession in a whorl of three from the base of the main axis. The present fungus has no resemblance to Triscelophorus, but rather the early stages of its conidium are like a Tricladium, especially the type species, T. splendens Ingold (Fig. 1 B). If Dendrospora is to be regarded as a natural rather than a form genus, the presence of dolipore septa in the present fungus would bar its inclusion in that genus. As most mycologists are trying to make taxa of Hyphomycetes as natural as possible, it would be helpful in future taxonomic studies on this group particularly the aquatic and aero-aquatic group where separation of genus and species is based mainly on conidial ontogeny and morphology, to examine routinely their septa for the presence of dolipore employing the simple staining technique mentioned above. The aquatic basidiomycetes Ingoldiella hamata Shaw and I. fibulata Nawawi produce conidia which are Tricladium-like in form and would have been placed in that genus had it not been for the presence of clamp connexions on their septate conidia. Another Tricladium described recently is T. malaysianum Nawawi. It was placed in this genus because of its similarity with other Tricladium spp. Its cells are binucleate, and dolipore septa are clearly seen in ammoniacal Congo red preparations.

Index Fungorum Number: IF312836

Figure 1. Dendrosporomyces prolifer. (A-E) Conidiophores with conidia at different stages of development arranged in a developmental series; (F-G) conidia from culture.