Vesicular-Arbuscular Mycorrhiza in the Gramineae

Abstract

VESICULAR-ARBUSCULAR mycorrhiza has been found to be widespread in cereals and in many grasses in Britain¹. The incidence of root infection and the amount of endophyte mycelium on the root surface and in the rhizosphere differ greatly in different habitats and communities. For example, in sanddune grasses—where mycorrhiza is strongly developed—the degree of infection varies between different species and with the stage in the dune succession. As illustrated in Table 1, samples collected from the sand dunes at Gibraltar Point, Lincolnshire, showed about a 20 per cent level root infection when growing in the embryo dune phase, that is on sites which have never supported plant growth previously. In the next zone in the dune succession infection falls almost to zero, but it reaches a maximum where the sand becomes stabilized in the fixed yellow dunes. In this zone, where the ranges of three grasses overlap, there is marked variation in infection between the different species. As the community matures and becomes more complex, there is a general decrease in endophyte activity. Roots of grasses in the fixed yellow dunes were often extensively covered with wefts of external mycelium as well as showing a high incidence of infection.