Observations on the genus Myrothecium

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OBSERVATIONS ON THE GENUS MYROTHECIUM II. MYROTHECIUM GRAMINEUM LIB. AND TWO NEW SPECIES

By N. C. PRESTON (With Plates XV and XVI and 5 Text-figures) INTRODUCTION

Three species of Myrothecium are dealt with here. Two of these, which are referred to in a previous paper (Preston, 1943), have not been previously described and are considered to be new. The third, Myrothecium gramineum, was originally named by Libert (1837) on the printed label ofa published exsiccatum. This species has been critically examined afresh and a fuller diagnosis of it is now presented.

Myrothecium gramineum Lib. (i) Material studied andcharacteristic features. Two collections of this species have been available. (a) An authentic Libert collection published in PI. Crypt. Ard. exsic. No. 380 on decaying grasses in Herb. R. B. G. Kew. The original description on this packet reads as follows: Myrothecium gramineum. Minutum rotundum in ambitu pilis erectis albis ciliatum ; disco subturgido nigro; sporidiis cylindricis. In Gramineis putrescentibus. Aestate. (b) On Pennisetum subangustum; Makene, Sierra Leone; F. C. Deighton (M. 1743); 28. i. 1939 from Herb. Imp. Myc. Inst, No. 1494. The most characteristic feature of M. gramineum is the very stout and usually aseptate setae (see Text-fig. IA) which fringe the sporodochium. These make it readily distinguishable from the new species, next described, which has somewhat similar spores (see Text-fig. 2) but the setae of which are comparatively slender and always multiseptate. (ii) Revised description Mycelium (on potato-dextrose agar). Pure white, forming a dense growth. Hyphae thin-walled, hyaline, septate; subaerial filament cells 20 x 3-4/-', aerial filament cells 20 x 1-2/-,. Sporodochia. Circular or elliptical, saucershaped, sessile, 0'2-0'9 mm. in diameter, 0'1-0'17 mm. deep. Black, surrounded by a fringe of numerous long, white, thick-walled setae. Setae. Straight, hyaline, tapering, ending in an acute or bluntly rounded point, generally continuous but occasionally with a single septum near the lower end about 40/-, above the base; 200 to about 400/-, in length, 10-20/-, wide near the rounded base and about 4/-,just below the tip, walls 3/-' thick at base tapering to about 1/-' at tip, inner surface of wall often slightly sinuous, outer surface occasionally so. Conidiophores. Composed of fertile hyphae and phialides. Fertile hyphae. Sub-hyaline, septate, olivaceous in the mass, 2-3/-' wide with the terminal (or sub-phialide) cells

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slightly broadening at the distal end; so closely intertwined as to be almost inseparable and forming a very compact sub-hymenial disk. Phialides. Hyaline, straight or flexuose, slightly clavate or sub-cylindrical, 8-15 x 2/-,; generally arising in whorls of three or more from the terminal cells of the fertile hyphae; those arising from the lower filaments longer than those from the uppermost ones, the whole forming a dense palisade-like layer in which the individual phialides are very difficult to distinguish. Conidia. Continuous, sub-hyaline or pale' green, narrowly ovate, ends rounded or with the broader end occasionally slightly flattened, 7-10 x 2/-" average 8'5 x 2/-'. Myrothecium jollymannii n.sp. (i) Material studied andcharacteristic features The type isolation of this species was originally made by F. W.Jollyman in 1936 from dried tobacco leaves in Nyasaland. A transfer was received from the Imperial Mycological Institute as Jollyman 145, 14. ix. 36. Further transfers from this have provided all the material upon which this description is based. The sporodochia bear a close superficial resemblance to those of M. inundatum and of M. gramineum owing to the fringe of stiff white setae which is common to each. The setae, however, are much more slender than those of M. gramineum and are multiseptate. They usually consist of seven to ten cells whereas those of M. inundatum, which are even more slender, rarely show more than five cells and the much more robust setae of M. gramineum are either continuous or have but a single septum a short distance from the base. The conidia are much larger than those of M. inundatum and more rod-like than those of M. gramineum, to which, however, they approximate closely in size. The brown sub-hymenial layer further distinguishes this species from any of those so far described in these studies; it occurs also in the new species M. striatisporum, next to be described, which, however, has very characteristic and easily recognizable conidia. Sub-cultures sometimes produce a wrinkled growth with very scanty aerial mycelium, if any at all, and usually without sporodochia. Myrothecium Jollymannii is a potential parasite since, like the British M. roridum, it readily attacked the living leaves and stems of Viola cornuta when spore suspensions were applied to detached shoots placed in a moist chamber. (ii) Description

Myrothecium jollymannii sp.nov, Mycelium ex hyphis hyalinis, tenuiter tunicatis, septatis compositum. Sporodochia orbiculata, sessilia vel brevissime stipitata, cupuliformia, 0'3I mm. diam., rarius ad 2 mm. diam. primo viridia demum atra, margine albido e setis hyalinis multiseptatis, crassetunicatis composito. Setae saepius 100-200/-, longae, 5-8/-' latae, 6-9/-' septatae. Conidiophora ex hyphis fertilibus phialidibusque composita. Hyphae fertiles olivaceobrunneae, irregulariter ramosae, dense intertextae, discum compactum

Observations on the Genus Myrothecium. N. C. Preston 273 obscuratum efficientes, septatae, infra septa paullo dilatatae, cellulis terminalibus quam basalibus brevioribus. Phialides subhyalinae, rectae vel curvulae, leviter clavatae, 12-15 x 2/L. Conidia continua, pallide olivaceobrunnea, cylindrica vel paullo angustata, apicibus obtusis, praecipue biguttulata, 8-12 x 2·S/L. A

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Text-fig. I. Setae. A, M. gramineum Lib.; B, M.jol?ymannii n.sp.; C, M . striatisporum n.sp. (A and B x 320; C x 1200.)

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Bah. Ex foliis siccantibus Nicotianae tabaei, in Nyasaland, Africa, in anno 1936 isolatum (F. W. Jollyman No. 145) et in agaro excultum et descriptum. P~rs exsiccata in H.erb. 1. M. 1. deposita sub. no. 1495 est typus. Mycelzum. HYI?hae thin-walled, colourless, 1-3fL wide; septate cells usually ID- I5fL In length. On artificial media sometimes forming a wrinkled growth closely appressed to the medium and consisting of tinted

Text-fig. 3. M .jollYmannii n.sp, Phialides from potato-dextrose agar culture.

Text-fig. 4. M . striaiisporum n.sp. Phialides.

Text-fig. 5. M. siriatisporum n.sp., approx. x 20. Sporodochium showing contorted fringing hyphae. Freehand drawing under Leitz 'Ultrapak'.

hyphae about 3fL wide of a pale brown, orange or pinkish colour, surmounted by a sparse aerial cottony growth, always pure white, consisting ofslender colourless hyphae 1-'2fL in width. Sporodochia. Circular, sessile or very shortly stipitate, cup-shaped, 0'3-1 mm., or occasionally '2 mm. in diameter, 0'15-0''2 mm. deep. Green at first becoming velvety black, surrounded by a rim of thick-walled, multiseptate, hyaline setae which at first curve inwards, then straighten. Setae. About IOD-'260fL long x 5-8fL wide, tapering to a blunt rounded point; usually of seven to ten cells which vary from 18-26fL in length with walls about IfL thick. Conidiophores com-

Observations on the Genus Myrothecium. N. C. Preston 275 posed of fertile hyphae and phialides (Text-fig. 3). Fertile hyphae. Olive brown, irregularly branched, septate, cells 8-15 x 2-4IL broadening slightly below the septa, the terminal cells shorter than the basal ones. Very closely intertwined forming a dark-coloured disk. Phialides. Sub-hyaline, straight or slightly curved, slightly clavate, 12-15 x 2IL. Conidia. Continuous, pale greenish brown, straight-sided, cylindrical or more usually very slightly tapering with blunt ends, the broader end flat the narrower end often somewhat rounded, generally biguttulate, 8-12 x 2'5IL, average 10 x 2·5IL.

Type isolation. From dried tobacco leaves, in Nyasaland, Africa, 1936 (F. W. Jollyman No. 145). Myrothecium striatisporum n.sp. (i) Material studied and characteristic features This fungus was originally isolated by J. C. Neil (No. 582) from a clay soil in New Zealand. A sub-culture of Neil's isolate was obtained through the Imperial Mycological Institute and this, together with subsequent transfers, has formed the basis of the present description. The sporodochia of this species (Text-fig. 5) are superficially indistinguishable from those of M. roridum, the white fringe being composed of twisted hyphae among which the presence of setae is very exceptional. Only once have any setae been found among the many hundreds of sporodochia examined (Text-fig. IC). Microscopically this species is readily distinguished by its striate, or fluted, conidia which are generally sub-fusoid though occasionally approximating to rod-shaped. It is further distinguishable from either M. roridum or M. verrucaria by the dark colour of the hymenial layer, and by the characteristic dark brown sterile filaments which are frequently found interspersed among the fertile hyphae, often extending beyond the general surface of the disk. (ii) Description Myrothecium striatisporum sp.nov. Mycelium ex hyphis hyalinis, tenuiter tunicatis, septatis 1-2IL diam. compositum. Sporodochia minuta, tenuiter cupuliformia, orbicularia vel irregularia, 0'05-0'2 mm. diam. saepe confluentia, primo viridia demum aterrima, margine albido ex hyphis contortis, hyalinis, tenuiter tunicatis, aliquanto latioribus composito. Setae rarissimae. Conidiophore ex hyphis fertilibus phialidibusque composita. Hyphae fertiles brunneo-tinctae, praecipue 3-septatae, irregulariter infra septa ramosae, ramis sursum dense intertextis, discum obscurum efficientibus; adsunt quoque hyphae steriles, non ramosae, atrobrunneae, inter hyphae fertiles crescentes. Phialides e subhyalino olivaceae, vel terminales vel e geniculo cellulae primogenitae oriundes, tenuissime clavatae, 7-22 x 3IL. Phialides terminales semper ceteris breviores. Conidia subhyalina deinde olivaceo-brunnea, continua, subfusoidea, apice acuta, basi minute apiculata, episporio primo laevi demum longitudinaliter striato ornata, 7 x 2'5 ad 12 x 3'5IL (av. 9.6 x 3IL)' lJab. Ex terra argillacea sub agro pascuo, in Nova Zealandia in 1937 18-2

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isolatum (J. C. Neil 582) et in agaro excultum et descriptum. Pars exsiccata in Herb. I. M. I. deposita sub. no. 1526 est typus . Mycelium. Pure white. Hyphae hyaline, slender 1-2p. wide, thin-walled, septate; cells 15-25P. long. Sporodochia. Minute shallow cups, circular or irregular, 0'05-0'2 mm. in diameter, about 0'05-0' 1 rnm. deep and often confluent into larger masses. Composed of loosely arranged hyphae, arising from a compact or pseudoparenchymatous base, and terminating in a dense disk-like layer. Green at first, becoming jet black surrounded by a white rim of rather broad, thin-walled, contorted, hyaline hyphae. Conidiophores composed of fertile hyphae and phialides (Text-fig. 4). Fertile hyphae. Tinted brown, consisting of a main axis usually of three cells with branches arising irregularly from below the septa and very closely intertwined. Cells 3-13p. long by about 2fL wide, the terminal cell always shorter than the others. Interspersed by unbranched, sterile, dark brown, thick-walled, somewhat sinuous filaments, 3""'4P. wide and 40p. or more in length (the walls of which frequently appear verrucose). Phialides. Subhyaline to pale olive green, greenish brown in the mass, arising terminally or from a geniculation of the parent cell, very slenderly clavate, rather thickwalled, 7-22 x 3P.. The terminal phialides short, straight or slightly flexuose, the lateral ones longer and bent sharply near the base, the whole thus forming a closely packed, even, hymenial layer . Conidia. Small, continuous, sub-fusoid, guttulate, broadest slightly below the middle, with the apex pointed and the base terminated by a minute stalk-like protuberance less than 1 p. long. Epispore at first smooth becoming fluted, usually with about fifteen ridges arranged longitudinally and often somewhat spirally. At first sub-hyaline, when mature smoky olive brown, 7 x 2'5- 12 )( 3·5p., average 9.6 x 3p.· Hab, Clay soil. New Zealand. The author wishes to thank the Director of the Imperial Mycological Institute for access to material in the herbarium and especially Mr E. W. Mason for his unfailing interest and helpful criticism; he is also greatly indebted to Miss E. M. Wakefield for the Latin diagnoses of the new species. REFERENCES No. 380. Genus Myrothecium Tode. I. The three classic species. Trans. Brit. myc. Soc. XXVI, 158-68.

LmERT, M.-A. (1837). Pl. Crypt. Ard. Fasc. IV, PRESTON, N. C. (1943). Observations on the

EXPLANATION OF PLATES PLATE XV Fig. I. MyrotJzecium gramineum Lib. ex Herb. R. B. G. Kew, Spores, x 1000. Fig. 2 . M. gramineum Lib. (Deighton M . 1743) ex Herb. I. M. I. Spores, x 1000. Fig. 3. M. ]olb>mannii n.sp, Sporodochia on agar, showin~ fringing setae, x 32. Fig. 4. M. ]olb'mannii n.sp, Fragment of sporodochium WIth setae, x 400.

PLATE XVI Fig. 5. M. ]ol~nnii n.sp, Fig. 6. M . striatisporum n.sp. Fig. 7. M. striatisporum n.sp. Fig. 8. M. striatisporum n.sp,

Conidiophores, x 1000. Small sporodochia showing fringing hyphae, x 60 approx, Spores, x 1000. Spores, showing striations, x 3000 approx.

(Acceptedfor publication 26 May 1947)

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