SOIL CONDITIONS AND THE ROOT‐INFECTING FUNGI

Summary An examination has been made of papers published during the last 15 years on soil‐borne fungus diseases of plants, with especial reference to the influence of soil conditions on infection. In reviewing the ecology of the root‐infecting fungi, a distinction has been made, following Reinking, between soil inhabitants and soil invaders. The soil inhabitants are considered to be primitive or unspecialized parasites with a wide host range; these fungi are distributed throughout the soil, and their parasitism appears to be incidental to their saprophytic existence as members of the general soil microflora. The soil invaders , to which class the majority of the root‐infecting fungi seem to belong, are more highly specialized parasites; the presence of such fungi in the soil is generally closely associated with that of their host plants. In the continued absence of a host plant, such fungi die out in the soil, owing to their inability to compete with the soil saprophytes for an existence on non‐living organic matter. This close association between the soil invaders and their host plants thus seems to be enforced by the competition of the general soil microflora. The influence of soil conditions upon a number of soil‐borne fungus diseases has been tabulated and discussed under the headings of soil moisture content, texture, organic matter, reaction and chemical composition. The relation of soil temperature to soil‐borne diseases has already been reviewed at length by L. R. Jones et al. (1926) and has therefore not been further considered here.