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Short Communications / Kort Mededelings

First report of Trichophaea abundans and the teleomorph of Peziza ostraco­derma associated with mushroom cultivation in South Africa

J.C. Coetzee* and A. Eickert • Department of Biological Sciences, Peninsula Technikon, P.O. Box 1906, Bellville 7535, Republic of South Africa

t Department of Botany, University of Pretoria, Pretoria 0002, Republic of South Africa

Received 10 August 1993; revised 8 December 1993

Trichophaea abundans (Karst.) Boud., its anamorph Dichobo­trys abundans Hennebert and the teleomorph of Peziza ostraco­derma Korf are reported from South Africa for the fi rst time. Without a microscopic examination these fungi are not easily distinguished from a number of other fungal contaminants of mushroom beds and care should be taken with the identification of these organisms.

Trichophaea abundans (Karst.) Boud., sy anamorf Dichobotrys abundans Hennebert en die teleomorf van Peziza ostracoderma Korf word vir die eerste keer uit Suid-Afrika vermeld. Sonder 'n mikroskopiese ondersoek is hierdie swamme moeilik van sommige ander swamme op sampioenbeddings onderskeibaar en versigtigheid moet by die identifisering daarvan aan die dag gele word.

Keywords: Chromelosporium (ulvum, Dichobotrys abundans, mushroom cultivation, Peziza ostracoderma, Trichophaea abundans.

'To whom correspondence should be addressed.

Trichophaea abundans (Karst.) Boud.:

During an earlier investigation (Coetzee 1987), dilution plates of what was preswned to be a pure culture of Chromelospor­ium fulvum (Linle Fr.) McGinty, Hennebert & Korf, obtained from the casing layer of an Agaricus bisporus (Lange) Imbach bed on a mushroom farm near Diepsloot in the Transvaal, resulted in single spore cultures with two distinctly different growth rates. Subcultures of the slower growing cultures grew into typical C. fulvum colonies but isolates of the faster growing colonies rapidly developed into abundantly sporulat­ing cultures of Dichobotrys abundans Hennebert, anamorph of the discomycete Trichophaea abundans. Initially, abundant apothecia were produced on potato-dextrose agar (PDA), con­firming the homothallic nature of this fungus as reported by Dodge (1922), Kevorkian (1932) and Tumau (1983), but with successive transfers the cultures progressively lost their ability to produce ascocarps and after only a few subcultures the teleomorph disappeared completely. After its initial isolation early in 1979, D. abundans was again encountered as a component of the aerospora on the Diepsloot farm at the end of May that year. A recent outbreak of D. abundans on the casing layer (steam pasteurized South African peat) of an A. bisporus bed at the University of Pretoria in September and October 1992 further indicated an association between this fungus and

S.-Afr.Tydskr.Plantk., 1994, 60(2)

mushroom culture. An isolate obtained from this latest out­break has been deposited in the National Culture Collection, Pretoria (anamorph; PPRI 4972). To the best of our know­ledge, this note represents the first report of T. abundans and its anamorph in South Africa.

As far as could be ascertained, T. abundans has been reported from mushroom beds on only two previous occasions. According .to Fagan & Fergus (1984), it was associated with black patches in mushroom compost where colonization by mushroom mycelium had failed to take place. Eicker et aI. (1989), who illustrated but erroneously identified T. abundans as Botrytis cinerea Pers. ex Nocca & Balb., reported it as a weed mould of the casing layer.

T. abundans is widely regarded as a pyrophilous or 'postfire' organism (EI-Abyad & Webster 1968a; 1968b; Tumau 1983; Egger & Paden 1986; Moore-Landecker 1988), and ascospore germination is stimulated by heat exposure (Dodge 1922; EI-Abyad & Webster 1968a; Turnau 1983). Due to this very nature of the fungus one would expect it to be well adapted to growth on the relatively competitor-free, steam pasteurized substrates of mushroom beds and it is rather surprising, therefore, that it has not been reported from these substrates more frequently. The authors suspect a much greater prevalence of this fungus on mushroom beds than is reflected in the li terature and believe that it might have escaped ,more frequent mention owing to incorrect identification and confu­sion with other fungi such as B. cinerea and "also C. fulvum. It is virtually impossible to distinguish between D. abundans and these fungi without the aid of a microscope, a fact mushroom growers should take cognisance of.

T. abundans produces hairy, greyish-white to buff apothecia of up to 3 mm in diameter. The operculate asci are iodine negative, containing eight uniseriate, biguttulate, smooth­walled ascospores each. A recent detailed and illustrated description of T. abundans apothecia is provided by Fort & Guarro (1986). T. abundans is, however, more readily recog­nized by its more abundant anamorph which is characterized by septate, dichotomously branching conidiophores ending in inflated, globose, terminal conidiogenous cells. The degree of conidiophore branching is dependent on the growth medium (Dodge 1922; Cain & Hastings 1956) and has, therefore, little diagnostic value. On each conidiogenous cell, a nwnber of simultaneously developing denticles are formed , each of which produces a solitary, globose, smooth-walled conidium at its tip. Conidia are ochraceous in mass. Due to the short terminal conidiophore branches, the conidiogenous cells are clustered

Figure 1 Sporulating conidiophores of Dichobolrys abundans. anamorph of Triclwphaea abundans. Bar represents 50 f.lm.

S.Afr.J.Bot.,1994,60(2)

together in compact groups, resulting in the botryose appear­ance of the conidiophores at the time of sporulation (Figure 1). Detailed, illustrated descriptions of D. abundans are provided by Dodge (1922), Kevorkian (1932), Cain & Hastings (1956), Hennebert (1973) and Fort & Guarro (1986).

El-Abyad & Webster (1968b) reported an optimum growth temperature of 30°C for T. abundans in soil tubes. Hardly any growth occurred at 37°C and at 15°C the growth rate was about 75% less than at the optimum temperature. In our own studies on PDA plates inoculated with conidia suspended in water, the same optimum was observed, with colonies reaching an average diameter (ten replicates) of 38.7 mm after about one and a half days. No growth occurred at l2°C, while at 17°C and 37°C, colony diameters of 9.3 mm and 29.9 mm, respectively, were measured. Very slight growth was still noticeable at 40°C. According to these results T. abundans could be expected to occur on mushroom beds during the spawn run periods before and after casing. It would, however, probably disappear after the temperature reduction necessary for sporophore initiation. The recent outbreak of D. abundans at the University of Pretoria coincided with a slight tempera­ture surge in the compost after casing due to a denatured guar protein meal supplementation.

The effect of T. abundans on A. bisporus has yet to be established. It has, however, been found to inhibit apothecial formation by Pyronema domesticum (Sow.) Sacco in soil (El­Abyad & Webster 1968b). The nature of this inhibition is not known but volatiles are unlikely to be the cause (Moore-Land­ecker 1988). Considering the findings of El-Abyad & Webster (1968b), it is reasonable to conclude, however, that the rapid growth rate of T. abundans enables it to rapidly colonize relatively competitor-free substrates, such as pasteurized mushroom compost and casing soil, in which it might then compete for the available nutrients. In this regard, Fagan & Fergus (1984 ) found T. abundans to be a more efficient producer of cellulose- and hemicellulose-degrading enzymes than A. bisporus, while it also produced enzymes involved in the degradation of lignin. According to these results, T. abundans seems very capable of competing with A. bisporus in mushroom compost. This, and the possible effect that this ftmgus might have on mushroom mycelium, are aspects requir­ing further investigation.

Pezjza ostracoderma Korf:

Since a previous report of the anamorph of P. ostracoderma (C. fulvum) in South Africa (Coetzee & Eicker 1983), the teleomorph has been encountered on mushroom beds in this country on a number of occasions but is reported here for the first time. Voucher specimens of the teleomorph preserved in FAA have been deposited in the National Collection of Fungi (PREM 51434). The role of this fungus in the mushroom industry has been reviewed by Coetzee & Eicker (1990).

The teleomorph of P. ostracoderma is characterized by fulvous to dark brown apothecia, usually 5 - 15 mm in diame­ter when fully expanded, but measurements of 20 mm, and in one case even 30 mm, have also been reported (Hennebert & Korf 1975). The brown pigmentation is restricted to the hymenium and in cross-section, the rest of the ascocarp appears more or less colourless. The eight-spored asci are iodine-positive and the mature ascospores are hyaline, biguttu­late and with reticulate wall markings. Detailed descriptions of

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this fungus are given in Schneider (1954) and Hennebert & Korf (1975).

From our involvement with the South African mushroom industry, it has become evident that, occasionally, difficulty is experienced with the identification of P. ostracoderma. This can primarily be attributed to the fact that it is impossible to identify this fungus on macroscopic characters alone, as is often attempted. Microscopic verification is imperative. P. ostracoderma is not the only brown apothecial fung~s occur­ring on mushroom beds and, as has been the experience, orga­nisms resembling P. ostracoderma may prove to be something quite different on microscopic examination (Coetzee 1987).

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