Plant Biology, University of New Hampshire, Durham, NH, USA, 03824

Background and objectives
The decomposer basidiomycetes rarely figure in lists of fungi isolated from litter or soil, and we still know little about the involvement in mineral cycling of these basidiomycetes, which are primarily decomposers of dead organic matter. As a first step in explaining the presence and origin, in decaying wood, of elevated levels of certain elements (particularly cations) not present in healthy wood, identification of species common to decaying wood and contiguous soil horizons is necessary. Since basidiomycetes are easily overlooked due to the presence of other faster-growing fungi or bacteria, media selective for basidiomycetes is essential in the isolation process. Various media have been used for isolations of basidiomycetes from soil [1] and wood-decay hymenomycetes [2, 3]. To ensure the maximum selectivity of basidiomycetes from both substrates, media were modified from those of previous researchers and tested on a variety of fungi and bacteria.

Materials and methods
Five different media were prepared for comparative growth of 20 basidiomycetes, 6 ascomycetes, including 3 yeasts, 6 deuteromycetes, 3 zygomycetes, and 1 bacterium. Media included: 1) MYA = 10 g malt extract, 2 g yeast extract, 20 g agar per liter distilled water, used as the control: 2) LGBDA = culture medium described by Thorn [1] plus the addition of 2 mg/L dichloran as described by Worrall [2]; 3) MYA1 = MYA + antibiotics of Thorn [1] + 2 mg/L each of benomyl and dichloran; 4) MYA2 = MYA + 2X antibiotics of Thorn [1] + 4 mg/L each of benomyl and dichloran; 5) MYBDA + MYA1, except amount of dichloran was 8 mg/L. Growth was measured as diameter of cultures in 100 x 15 mm petri plates at regular intervals over a 4-week period.

Results and conclusions
The control medium (MYA) supported measurable and in most cases substantial growth of all organisms tested. Fourteen basidiomycetes grew slowest on LGBDA, 4 did not grow at all, and 2 grew only on this medium and the control medium. MYBDA was the most effective in restricting fast-growing zygomycetes and deuteromycetes, and supported growth of all basidiomycetes with the exception of the 2 which grew only on LGBDA. Non-yeast ascomycetes grew only on MYA. Ascomycetous yeasts did not grow on MYBDA and grew very little on all other media. The bacterium grew only on MYA. To ensure the isolation of the most basidiomycetes in felled wood and contiguous soil profiles, and to maximize restriction of fast-growing non-basidiomycetes, both LGBDA and MYBDA were selected as the media of choice for further studies.

1. Thorn RG, Reddy CA, Harris D, and Paul EA, 1996, Appl. Environ. Microbiol. 62, 4288-4292.
2. Worrall JJ, 1991, Mycologia 83, 296-302.
3. Johnson GC, 1995, Can. J. Microbiol, 41, 104-107.