A QUANTITATIVE STUDY OF MYCORRHIZAL INFECTION IN TRIFOLIUM: SEPARATE DETERMINATION OF THE RATES OF INFECTION AND OF MYCELIAL GROWTH

Abstract

We present a simple mathematical model of the infection of roots of Trifolium subterraneum by vesicular‐arbuscular mycorrhizal fungi. The model permits separate calculation of the following. (1) The frequency of infection in unit length of root in unit time from mycorrhizal propagules distributed uniformly and randomly in soil. A value of 40·8 m−1 day−1 was found for the soil used in the experiments. (2) The rate of fungal growth along the root cortex from a single entry point, which was found to be 12·2 × 10−4 m day−1 for infections derived from propagules in the same soil. An alternative method of estimating the frequency of infection close to the root tip (from measurements of the rate of root growth and distance between the apex and the most apical entry‐point) is presented. Comparison of values obtained suggests that the root tip is nearly 10 times more infectible than the average for the whole root system. Some of the assumptions implicit in the model have been investigated experimentally and the results are reported here. The model should be useful in distinguishing between environmental effects on the phases of colonization occurring in the soil, and at the root surface and within the root. Copyright © 1981, Wiley Blackwell. All rights reserved