Common culture media such as PDA, SDA are routinely used in fungus study.
I found in many articles that the authors had used half- or quarter strength of the media. How lowering strength helps fungi culture?
Is it slow down the growth and sporulation?
Thanks in advance.
As fungi was put in culture they tend to undergo phenotypic changes these include loss of virulence from the wild type original culture.
These changes accelerate and are more pronounced under nutrient rich media.
Full strength PDA a popular general media uses a high nutrient level which facilitates quick colony development with observable phenotypic development aiding in identifications.
The reduction of nutrient levels helps conserve wild type phenotypes and virulence factors. Good for the conservation not good for quick phenotype identification.
Conservation methods almost always include weaning a culture for high nutrient and putting them in lean media.
In general terms the faster the growth and develop the quicker that key characters can change losing the original pheno and geno type which is desired.
In addition to the phenotypic (and genotypic) changes that can occur on high nutrient media (as Paul Hepperly noted), there also are impacts of nutrition on sporulation and secondary metabolite production.
Some fungi sporulate better or faster under low nutrient than high nutrient conditions, so for these fungi, a reduced strength medium can improve identification and/or production of spores for inoculum preparation. This will depend on the species (e.g. https://ac.els-cdn.com/S0953756206002607/1-s2.0-S0953756206002607-main.pdf?_tid=fe745963-7c1a-435b-8db4-00f7fe0f5c6d&acdnat=1536685831_7a62b24d2d989c8db1eba4931e843664). You also can get more variability in spore and sporophore shapes and sizes on high nutrient media, so for consistent size and shape for fungal identification and characterization, a lower nutrient medium may be recommended (e.g. Leslie & Summerell 2006).
The medium also can influence secondary metabolite production (e.g. https://mmbr.asm.org/content/mmbr/66/3/447.full.pdf, Boerrema et al. 2004, etc.). Thus researchers often adjust nutrient levels, or use different media, to enhance or reduce production of secondary metabolites of interest or concern.
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