Sporulation of Fungi inside the Plant Host Cell

Abstract

THE sporulation of fungi usually occurs when suitable conditions of nutrition and aeration are provided. It appears that whereas the conditions inside plant cells commonly admit of the formation of resting spores, they are, in general, less suitable for the formation of non-resting ones. Thus in Plasmodiophorales, the plasmodia develop into resting spores within the host cells, whereas the active swarm spores are typically formed outside the host. Again, in Pythiaceae, Albuginaceae and Peronosporaceae, the resting spores (zygotes) may be formed inside the host tissue; but the zoosporangia and conidia are usually formed outside it. The powdery mildews, smut and rust fungi, in different ways, exemplify this same phenomenon. So far as I know, conidia as defined by Mason1 are rarely reported to be formed inside plant cells and, more particularly, at some depth in a tissue matrix. In these few cases where they have been reported, they typically occur inside the vessels, for example, microconidia of Fusarium oxysporum cubense inside the spiral vessels of banana plants2, and the presence of microconidia of Fusarium oxysporum conglutinans has been described in the xylem of the cabbage plant3. It may be that it is not uncommon in the experience of pathologists to encounter conidia in plant cells; but the phenomenon does not appear to have been given much attention and it has not been dealt with in standard texts.