Abstract
Traditionally, fungal growth dynamics were assessed manually, limiting the research to a few environmental conditions and/or fungal species. Fortunately, more automated ways of measurement are gaining momentum due to the availability of cheap imaging and processing equipment and the development of dedicated image analysis algorithms. In this paper, we use image analysis to assess the impact of environmental conditions on the growth dynamics of two economically important fungal species, Coniophora puteana and Rhizoctonia solani. Sixteen environmental conditions combining four temperatures (15, 20, 25 and 30 °C) and four relative humidity (RH) conditions (65, 70, 75 and 80% RH) were tested. Fungal growth characteristics were extracted from images of the growing fungi, taken at regular points in time. Advanced time series analysis was applied to quantitatively compare the effect of the environmental conditions on these growth characteristics. The evolution of the mycelial area and the number of tips over time resulted in typical sigmoidal growth curves. Other growth characteristics such as the mean hyphal segment length did not vary significantly over time. Temperature and RH usually had a combined effect on the growth dynamics of the mycelial area and the number of tips. When defining optimal growth conditions for a fungus, it is therefore of primordial importance that the effect of temperature and RH is assessed simultaneously. At the most extreme conditions we tested, the mycelium most probably experienced water stress when developing over the inert Petri dish surface. An RH of 65% (independent of temperature) for C. puteana and a temperature of 30 °C (independent of RH) for both C. puteana and R. solani therefore always resulted in limited fungal growth, while the optimal growing conditions were at 20 °C and 75% RH and at 25 °C and 80% RH for R. solani and at 20 °C and 75% RH for C. puteana. The method applied in this study offers an updated and broader alternative to classical and narrowly focused studies on fungal growth dynamics, and is well suited to efficiently assess the effect of environmental conditions on fungal growth.
Highlights
Fungi are ubiquitous and grow even in the most extreme environments (Cooke 1968)
Vertical growth of the hyphae was limited and fungal growth was essentially restricted to two dimensions, which is a prerequisite for applying the image analysis procedure described below
General fungal growth dynamics Several fungal growth characteristics were assessed over time for each species (Fig. 2.3)
Summary
Fungi are ubiquitous and grow even in the most extreme environments (Cooke 1968). Each fungal species grows under a particular range of environmental conditions. Fungal growth characteristics, such as colony radius (Etheridge 1957; Boddy 1983; Pasanen et al 1991), the growth rate (Bonner and Fergus 1960; Ayerst 1969; Magan and Lacey 1984; Gock et al 2003) or the number of germinated spores (Tommerup 1983; Huang et al 2001) can be derived directly from such images Up to this day, these analyses are often performed manually, an image analysis method is for instance available for measuring the mycelial area (Ancin-Murguzur et al 2018). Even though several studies compare the effect of environmental conditions on fungal growth over a certain period of time (Etheridge 1957; Magan and Lacey 1984; Pasanen et al 1991; Nielsen et al 2004), no elaborate time series analysis is performed to underpin the comparison
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