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  Eur.J.Hortic.Sci. 82 (1) 3-11 | DOI: 10.17660/eJHS.2017/82.1.1
ISSN 1611-4426 print and 1611-4434 online | © ISHS 2017 | European Journal of Horticultural Science | Original article

Use of ergosterol as an indicator for colonization of peat-based growing media by saprophytic fungi

D. Lohr, Ch. Woeck and E. Meinken
Weihenstephan-Triesdorf University of Applied Sciences, 85350 Freising, Germany

SUMMARY
During the last decade colonization of peat-based growing media by saprophytic fungi such as Peziza ostracoderma is of increasing concern. Due to its unpleasant appearance and possible harmful effects on plants and humans, batches of raw materials with a high risk for fungal colonization should be excluded from production of growing media. However, no suitable method for quantifying fungal biomass in growing media constituents exists. In soils and cereals ergosterol – a sterol quite specific for fungi – is used as indicator for fungal biomass. The aim of the current research was to adapt a method for analysing ergosterol in peat-based growing media. Based on a literature review an analytical procedure for extraction of ergosterol from peat-based growing media, purification of extracts and subsequent measurement by HPLC-UV was specified. This analytical procedure was validated and finally applied to various peat-based growing media and peat substitutes as composts or coir pith after inoculation with mycelia of Peziza ostracoderma. After an ultrasonic-assisted extraction with a methanol/ethanol mixture and purification with n-hexane, ergosterol is measured by HPLC-UV. The method has a high repeatability and linearity. Limits of detection and quantification of 0.6 mg g-1 and 2.4 mg g-1, respectively, are quite low. The analysis of mixtures from two peat samples in varying ratios – one not colonized and one heavily colonized by Peziza ostracoderma – indicates that the method is a promising approach to quantify intensity of fungal colonization. Analysis of various growing media constituents and growing media in conditions as delivered as well as after inoculation with Peziza ostracoderma and subsequent incubation for twelve days demonstrated that the method can be used to asses fungal colonization of different growing media constituents. The analytical procedure is quite fast and easy and has low technical requirements but at the same is highly precise. Thus, it is a promising tool for assessing the risk of fungal colonization of peat-based growing media and growing media constituents.

Keywords fungal biomass, HPLC-UV, Peziza ostracoderma, ultrasonic-assisted extraction (UAE)

Significance of this study

What is already known on this subject?

  • Ergosterol is a cell wall compound found in fungi and certain microalgae and protozoa but not in bacteria, insects or plants. Thus, ergosterol is a commonly used indicator of fungal biomass e.g., in food and soil sciences. Ergosterol is analysed by HPLC-UV after extraction with organic solvents. The extraction procedure is done in different ways as refluxing microwave digestion or ultrasonic-assisted extraction.
What are the new findings?
  • A procedure for analysis of ergosterol in growing media was developed. The procedure is very precise and has a high repeatability as well as a low limit of detection. Furthermore, due to its high throughput and low technical requirements the method is suitable for routine testing.
What is the expected impact on horticulture?
  • Colonization of growing media by saprophytic fungi is an increasing problem. The analysis of ergosterol might be a valuable tool to assess this risk and help growing media manufactures to initiate countermeasures before the fungal colonization becomes visible.

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E-mail: elke.meinken@hswt.de  

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Received: 10 October 2016 | Accepted: 20 December 2016 | Published: 23 February 2017 | Available online: 23 February 2017

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