THE DEVELOPMENT OF MYCORRHIZAL POPULATIONS ON POT‐GROWN SEEDLINGS OF EUCALYPTUS ST‐JOHNII R.T. BAK

Abstract

The development of a population of mycorrhizas on the root system of a pot‐grown Eucalyptus seedling has many of the characteristics of a disease epidemic. For example, the number of mycorrhizal apices tends to increase exponentially in the early stages. The disposition of these mycorrhizal apices is non‐random, a fact which should engender care when sampling during field surveys. The final pattern of distribution of mycorrhizal apices within the root system reflects the degree of pre‐infective ectotrophic spread, the frequency and location of primary infection events, the perpetuation of mycorrhizal apices by forward growth, the extent to which they proliferate by branching, and the contribution of later secondary infections from mycorrhiza‐derived inoculum. The relative importance of these different processes is determined, as in a plant disease, by interaction between prevailing fungal, plant and environmental factors. The importance of inoculum availability and the capabilities of the fungus with respect to different regions of the root surface are stressed. The different modes of origin of mycorrhizal apices must be taken into account in any studies which seek to understand the mechanisms involved in conversion of normal root apices into mycorrhizas. Copyright © 1982, Wiley Blackwell. All rights reserved