American Midland Naturalist 109(2): 406-408 (Apr 1983)
The Mycorrhizal Status of the Cruciferae
Richard J. Medve

Examination of 25 crucifer taxa, representing 15 genera and 24 species, showed that one species in each of two genera was mycorrhizal. Lobularia maritima and Lunaria annua were both infected with the vesicular-arbuscular type of mycorrhiza. This study extends the list of crucifers examined for mycorrhizae to 36 species and the number of known mycorrhizal crucifers to eight species in six genera. In most cases the number of vesicular-arbuscular structures was sparse and the percent of infection low. Although early investigators considered the Cruciferae to be nonmycorrhizal, recent evidence indicates that a degree of mycorrhization does occur in some species of this family and those few species may be facultative mycotrophs.

Crucifers contain certain sulfur compounds that are toxic to fungal spores and mycelium (see Iqbal and Qureshi, 1976). A sulfur-free variety of Brassica napus, however, when grown in the presence of wheat, formed V-A mycorrhizae (Iqbal and Qureshi, 1976). Bevege and Bowen (1975) found that Endogone spores did not germinate in association with Arabidopsis thaliana. These two studies indicate an allelopathic effect by crucifers on potential mycorrhizal-forming fungi. Genotypic differences in fungal infection susceptibility may occur within some species and could account for high infection rates of a single cultivar or very low rates for a species in general. As a group, the Cruciferae appear to be nonmycorrhizal, and the few mycorrhizal specimens found to date may represent these infrequent genetic variants. At best, a few crucifer species may be weak facultative mycotrophs. Janos (1980) described conditions where facultative mycotrophic species survive in very infertile soils, but may never support much infection. The ruderal habit of many crucifers, their common occurrence on fertile farmlands which are known deterrents to mycorrhizae formation, and the infrequent occurrence of fully developed mycorrhizae add further support to the hypothesis that the few crucifer species that are mycorrhizal are, at best, weak facultative mycotrophs.

Mycorrhizal Fungi