2.1 Measurement methodologies
In order to describe and quantify hyphal growth and branching, measurement of the parameters hyphal diameter, hd, and hyphal length, hl, is essential. These allow hyphal volume, hv, to be calculated, which when multiplied by the average density of the composite hyphal material, ρ, gives an estimate of biomass, X. If these measurements are taken over a series of time intervals it is possible to calculate hyphal extension rate, E, and thence rate of increase of biomass. Currently, automated image analysis systems permit real-time analysis of these microscopic parameters (Adams & Thomas, 1988). Some of these analyses suggest that hyphal tips grow in pulses (Money, 2001), although this has been contested Jackson, 2001), particularly because the observations use video techniques and the pixelated image generated by both analogue and digital cameras will cause pulsation artefacts (Hammad et al., 1993).
The most important macroscopic parameter is total biomass. Total hyphal length is proportional to total biomass, if hd and ρ are assumed to be constant; but measurement can be difficult. Non-destructive direct mass measurement is rarely feasible, in most cases due to the technical difficulty (and sometimes impossibility) encountered in physically separating the mycelium from the substratum. Acuña et al. (1998) developed a neural network that they trained to correlate colony radius with colony biomass. However, this relationship is only relevant to circular mycelia and measurements in two dimensions. More general relationships with biomass have been suggested for particular chemical compounds, the most promising of which is ergosterol, a sterol characteristic of fungal membranes (Desgranges et al., 1991; Katz et al., 1972).
Updated December 7, 2016