Infection of plants by Corticium solani and C. praticola—Effect of plant exudates

The parasitism by two strains of Corticium solani (Prill. & Delacr.) Bourd. & Galz. and one of C. praticola Kotila has been investigated. A lettuce strain of C. solani parasitized lettuce but not cabbage: a cabbage strain parasitized cabbage but not lettuce. C. praticola parasitized both. Wheat was not parasitized by the strains of C. solani but was parasitized to a limited extent by C. praticola.

Exudates from the roots of cabbage seedlings stimulated the growth of each of the three fungi to the same extent. Exudates from lettuce seedling roots also did this but the effects were much more striking. Wheat root exudates had very little effect on the growth of either of the fungi. These results refute the hypothesis that exudates are an important factor in the specificity of parasitism of different strains of C. solani.

When exudates from roots of different ages were examined it was found that those secreted in the first week after sowing seed were much more effective than those secreted in the second and third weeks.

Root exudates did not stimulate the formation of infection cushions on pieces of epidermis from different host plants in any way that could be correlated with specificity of parasitism. But infection cushions were formed much more abundantly on pieces of epidermis taken from susceptible as compared with resistant plants. In general the cushions formed on epidermal strips were not so highly developed as those formed on intact hypocotyls.

The significance of these results is discussed.