A Study of the Kinetics of Hyphal Extension and Branch Initiation of Fungal Mycelia

Abstract

Growth of Mucor hiemalis, Geotrichum candidum, Aspergillus nidulans, Neurospora crassa and Penicillium chrysogenum was studied by time lapse photography. The total hyphal length of the mycelium of each species increased at an exponential rate; in M. hiemalis exponential growth continued until the mycelium had a total hyphal length in excess of 10 mm. After spore germination there was an initial phase of discontinuous tip production followed by a phase of ‘continuous’ tip production. The hyphal length and number of tips possessed by a mycelium increased exponentially at approximately the same specific growth rate. The amplitude of the oscillations in the length of the hyphal growth unit of a mycelium decreased progressively during mycelial growth and eventually the growth unit attained a more or less constant value. The results support the hypothesis that mycelial growth involves the duplication of a ‘growth unit’ which consists of a tip and a certain mean length of hypha.