A chytrid on Dacrymyces

Notes and brief articles Tremellales. State University of Iowa Studies in Natural History 19, 1-122. MOLLER, A. (1895). Protobasidiomyceten. jena, Germany: Botanische Mittheilungen aus den Tropen, vol. 8. OLIVE, L. S. (1975). The Mycetozoans. New York and London: Academic Press.

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REID, D. A. (1974). A monograph of the British Dacrymycetales. Transactions of the British Mycological Society 62, 433-651. RICK, J. (1958). Basidiomycetes Eubasidii in Rio Grande Do Sul-Brazilia. Iheringia ser. bot. 2, 1-56.

A CHYTRID ON DACRYMYCES BY HILDA M. CANTER

Freshwater Biological Association, Ambleside, Cumbria, LA22 oLP AND C. T. INGOLD 11

Buckner's Close, Benson, Oxford, OX9 6LR

A monocentric, eucarpic, epibiotic chytrid, possibly referable to Rhizophlyctis, is described parasitizing the arthroconidia of Dacrymyces stillatus. In a collection of Dacrymyces stillatus Nees: Fr. from Swyncombe Downs, south Oxfordshire

Fig.

1.

(made by C.T.I.) in January 1982, a chytrid was found in the orange conidial sporophores apparently

Rhizophlyctis sp. associated with arthroconidia of Dacrymyces (a), very early stage in sporangia! growth;

(b--d) immature sporangia bearing several rhizoidal axes; (e-f) sporangia with a dehiscence papilla; (g) empty

sporangium. Live materia! drawn by C.T.I.

Trans. Br. mycol. Soc. 82 (4), (1984)

Printed in Great Britain

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Figs 2-14. Rhizophlyctis sp. 2-3, Habit of sporangia among the arthroconidia; 4, Recently germinated zoospore; 5, Two rhizoidal axes each with a small swelling (arrowed) at the point of contact with the arthroconidiwn; 6, A large sporangiwn; 7-10, Sporangia with dehiscence papillae, in 8, two other thalli (arrowed); 11, Empty sporangium; 12-13, Possible sac-like, endobiotic rhizoid (arrowed); 14, Thallus with a thick wall (? resting spore). Live material, Magdala Red stain added to 2,10,12,13. Fig. 3 x 1100; 2, 7, 7 x 1600; rest x 2000. Photographed by H.M.C.

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a..a;.....

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-" 19

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Figs 15-26. R hiz ophly ctis sp. 15-22, zoos po res ; 15, Cent ral clu ster of globules and posteriorly placed con tract ile vacuole (arrowed) clearly visib le ; 16, 17, Co ntractile vacuole open and 18, closed ; 19, Zoospor e with m inute, peg-like pseudopod; 20, Elongate , basal pseudop od (out of focu s) represen ted by ' wh ite ' area exte ndi ng downwards fr om place of flagellum attachment ; 21-22, Creeping zoospores ; 23 , Swelling at di stal end of a dislodged rhizoidal axis ; 24-26, Empty sporangia. Live material x 2000, phase-contrast. Phot ographed by H.M.C. MYC 82

742

Notes and brief articles

parasitizing the arthroconidia , The latter are (F igs 15, 17 ). In Figs 16, 18,22 where they are not typically two-celled, and in water mounts they tend in focus their position is indicated photographically, to remain together in short chains. They are orange under phase-contrast illumination, by a large white due to the presence of a carotene which is area in the protoplasm which itself appears dark responsible for the colour of the conidial grey. At the posterior end of the zoospore a minute contractile vacuole ( 1' 5 flm diam) could be seen sporophore. The fungus (Fig. 1 a-g) occurred in the viscous (F igs 15, 17) made conspicuous by its rhythmical slime between the branched threads of arthro- enlargement and disappearance. The single posconidia. Each chytrid, when fully grown, consisted teriorly-directed flagellum was about 17 flm long of a nearly spherical zoosporangium (4- 12 flm and terminated in a whip-lash. The point of diam) from the surface of which two to eight fine attachment of the flagellum to the zoospore rhizoids grew out. These rhizoids, up to 25 fl m sometimes appeared sub-basal (F ig. 22 ) rather than long, were simple (F ig. 1 e) or branched (F ig. 1 b) basal. Zoospores both with and without flagella and usually made contact with the arthroconidia. were seen to creep in an amoeboid manner (F igs Young stages in the growth suggest that the 1~22 ). germinating zoospore at first produces one (F ig. 4) A number of spherical thalli, 7-11 flm d iam , or possibly two (F ig. 5) rhizoidal threads and that crowded with minute globules and surrounded by additional rhizoids arise later. Sometimes a rhizoidal a somewhat thickened smooth wall (F ig. 14 ), were thread became slightly inflated at its point of noted. Possibly such specimens represent a resistant contact with an arthroconidium (Figs 5,23). The stage of the fungus. Very few phycomycetes have been recorded on contents of most of the cells to which a rhizoid had become attached were disorganized (F ig. 1), but the members of Basidiomycotina (Spar row 1960; Barr presence of an endobiotic rhizoidal system has not & Bandoni, 1979) and none previously on yet been demonstrated with certainty. However, Dacrymyces. occasionally a small, walled, sac-like structure, Although several aspects of the life-cycle of the which appeared to be an internal continuation of chytrid described above remain incompletely the external rhizoid, was observed within a host cell known, the overall thallus structure suggests that it (F igs 12-13). Such sacs took on a pink colouration might find a place in the genus Rhizophlyctis A . when placed in Magdala Red stain and are believed Fischer. The rose-red colouration of the sporangia to be d istinct from the vacuoles of similar shape could point to it being a small form of the ubiquitous Karlingia rosea (de Bary & Woronin) which occur in healthy arthroconidia. When mature, the content of the sporangium, Johanson, but neither exo- nor endo-opercula, comprising many small globules, took on a faintly which presently characterize this genus, have been rose-red colouration. A single, protruding de- observed. hiscence papilla (F igs 1 e-f, 9) was usually formed, We express our thanks to Mrs J . C. Rhodes for but there were sometimes two (F ig. 8) or three. The wall of a papilla remained thin and delicate at its typing the manuscript. apex (F ig. 10). Dehiscence was not observed, but as no remains of a detached lid were ever found, the REFERENCES fungus is thought to be inoperculate. After the liberation of zoospores, empty sporangia retained BARR, D . J. S. & BANDONI, R . (1979) . A new species of Rozella on a Basidiomycete. M y cologia 71, 1261-1264. their shape (F igs 11,24-26). SI'ARROW, F . K. (1960) . Aquatic Phycomycetes, znd Occasionally a few zoospores were seen swimming revised edn. University of Michigan Press, Ann Arbor, amongthearthroconidia (Figs 15-18). The zoospore U.S.A. was ovoid, 5 x 2' 5-6 x 3 flm, and as it swam its body rocked from side to side or sometimes rotated. A cluster of about four small refractive globules occupied a central position within the zoospore

Trans . Br. myc ol. Soc. 82 (4), (1984)

Printed in Great Br itain