Most fungi have evolved on solid matrices, and hence solid media are generally better than liquid media in terms of quantity and number of metabolites produced. On agar media, any contamination is usually visible, and an agar plug technique can be used to sample different parts of the fungal colony and its surroundings.
In general, agar media for optimal secondary metabolite and mycotoxin production have been based on media containing yeast extract. Yeast extract sucrose (YES) broth was introduced as a "semisynthetic" broth medium for aflatoxin production by Davis et al. (1966). It was later shown to be a very effective general secondary metabolite production medium when used with a crude yeast extract (DIFCO or SIGMA) and formulated as an agar medium (YES agar) by Frisvad (1981); Frisvad and Filtenborg (1983), and has been used for Penicillium, Aspergillus, Fusarium, Alternaria, and many other fungal genera (Andersen et al. 2002; Thrane 2001). Other media including Czapek yeast autolysate (CYA) agar, Potato dextrose (PD) agar can be used to supplement YES agar, depending on the genus being considered, as seen in Table 1. Some of these semisynthetic agar media can occasionally give problems as certain brands of yeast extract, malt extract, potato extract, agar, peptone, or tryptone, etc. may differ significantly in composition, although this may be diminished by adding trace elements and magnesium sulphate (Filtenborg et al. 1990).
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