Naiadella fluitans

Naiadella fluitans Marvanová & Bandoni 1987, in Marvanová & Bandoni, Mycologia, 79(4), 578-586 (1987)

Etymology:  Fluitans (Lat.) = floating, because of dispersal of conidia on water.

Diagnosis: Colonies (MA, MYP) growing slowly (ca. 2-3 mm/30 days at 15 ^oC), remaining restricted, creamy to white. Laccase reaction positive (violet); tyrosinase negative. Aerial mycelium typically abundant, dense, delicate, downy, usually covering the entire colony, margin irregular; substrate mycelium forming a tough layer, with pale ochraceous tinge. Hyphae hyaline, geniculose, thin-walled, 1.5-4 µm wide, primary septa clamped, secondary septa abundant and clampless, medallion clamps sometimes present; pore of clamped septa with a small central inflation visible after staining with ammoniacal Congo Red. Advancing hyphae undulate, mostly unbranched when young, the aerial hyphae frequently branched, the branches of two types, many short, perpendicular, determinate, at right angles to the main axis and clampless, sometimes aggregated at the hypha! tips in a sympodial or irregular arrangement (Figure 2B), others indeterminate, arising from clamps on the main axes and typically clamped near their origin. Substrate hyphae profusely lobed. Haustoria) branches (Figure 2A, 3C-E) typically borne on short stalks and with either one or two basal clamps, the main cell binucleate, 9-12 µm long, 2.5 µm diam near the base, narrowly obclavate or tapering distally, with 1(-2) terminal filaments, the latter ca. 1 µm diam and up to 20 µm long, 1-3 shorter filaments sometimes present basally. Sporulation infrequent, sporadic, or not found on most agar media, on sterilized S. microcarpus litter, or in aerated water, abundant in standing water and in the perfusion chamber; commonly present on OF A, occurring at times on W A, and on MYP in association with contaminants. Conidiophores single, similar to hyphae, apical or lateral, determinate, or proliferating sympodially, up to 4 µm wide. The first conidiogenous cell terminal, each subsequent one arising through proliferation of the basal clamp of the preceding cell, the clamps forming a staircase-like series, each step with an empty or developing conidiogenous cell (Figure 1E-H, 4A, B); the wall of the fusiform portion of the conidiogenous cell is slightly thicker than that of the neck, the latter usually having a lacerate margin after conidium release. Conidia solitary, apical, navicular or obclavate, (18-)25- 32(-45) x (4-)5-6.5(-9) µm, the base truncate and with an inconspicuous frill (Figure 1A, B), typically with 3-4 branches, these synchronous, bristle-like, sometimes slightly narrowed basally, devoid of cytoplasm at maturity and often with one or more retraction septa, 15-27 x 0.5-1.5 µm; apical branch single, in line with the longitudinal conidium axis, straight; lateral branches 2-3, opposite or verticillate, inserted ca. 5-7µm below the conidial apex, divergent, straight or pendulous. Conidial secession rhexolytic; germination (Figure 2D) occurring through the basal septum, laterally near this septum, or less frequently near the branches, all of the cytoplasm of the conidium migrating into the germ tube; 1-4 retraction septa may appear in the conidial body as evacuation occurs. Conidia from agar cultures are like those from water, but may have 1-5 branches. Such conidia sometimes have 1-3 suprabasal branches directed posteriorly (Figure. 1B, 3H). Cultures examined: R. J. B. 7484-A, from the type locality, Canada; CCM F-14386, from stream foam, Moravian Kars, near Bmo, Czechoslovakia. Isolate CCM F-14386 differs from 7484-A in some minor features, e.g., the conidial body is often apparently narrowed and elongate distally and hence is longer (up to 45 µm as compared with the maximum of 35 µm in the isolate from Canada). Occasionally the apex may be divided two to three times (Figure 2C). During germination, 2-4 retraction septa develop in the conidia; 0-2 are present in germinating conidia of 7484-A. Development of conidia of 7484-A, as observed in the perfusion chamber at ca. 18 ^oC, is illustrated in Figure 2E. The conidial primordium appears as a bud on the apex of the conidiogenous cell. An inconspicuous interruption of the outline of the cell wall on the neck between the conidiogenous cell and the conidial initial is seen and may suggest enteroblastic ontogeny. The conidial primordium enlarges, gradually becoming ellipsoidal or clavate and, finally, obclavate. At this stage, the cytoplasm in the conidiogenous cell starts to become vacuolate basally; delimitation of the conidium takes place by deposition of a septum somewhat above the point where the conidial base might be expected according to the morphology of the primordium. While vacuolation continues, the last residue of cytoplasm gathers in the upper part of the conidiogenous cell, suggesting transport into the conidium. The branches usually are initiated at the beginning of vacuolization; they are cellular in development (Sutton, 1981), and continuous with the conidial body when immature. During maturation, cytoplasm retracts from the bristle-like branches and 1-2 retraction septa are deposited. The complete differentiation of a conidium under these conditions requires ca. 20-24 hours. Secession is tardy; it takes place somewhat below the delimiting septum, approximately at the point of the presumed conidial base. Detached conidia did not germinate on the water surface or in water, but did so freely on a thin layer of MA. Unlike other hyphomycete conidia, they did not swell noticeably on germinating. As the protoplast emptied into the germ tube near the truncated conidial base, retraction commenced at the distal end (Figure 2D). Retraction, accompanied by deposition of adventitious septa, was also observed to continue in the primary hypha. The first clamp occurs usually at ca. 100 µm from the conidial base, and branches of the primary hypha usually developed after this.

Index Fungorum Number: IF131815

Figure 1. Naiadella fluitans (R. J. B. 7484-A). A. Conidia from water. B. Conidia from agar (note the variable number of branches). C, D. Simple conidiophores with integrated conidiogenous cells and developing conidia. E-H. Simple or branched conidiophores with discrete fusiform conidiogenous cells formed successively and with basal clamps (note the empty conidiogenous cells). (A, C-H, from submerged culture; B, from malt agar). Scale = 20 µm.

Figure 2.  Naiadella fluitans (A, B, D, E, from R. J. B. 7484-A; C from CCM F-14386). A. Haustorial branches on hyphae. B. Ends of hyphae showing sympodial branching. C. Sketch of conidia from agar. D. Germinating conidia (note protoplast migration and the retraction septa in the conidial body). E. Development of a conidium as observed in the perfusion chamber. (A, B, submerged culture; D, malt agar.) Scale for A, B, E = 20 µm; for C, D, scale = 50 µm.