Brigitt BERGER
(Institute of Agronomy and Plant Breeding, University of Gottingen, Germany)
Green-house cultures of Arabidopsis thaliana and some related species (A. suecica, A. arenosa) can be destroyed completely by Alternaria brassicae. Older leaves lying near the soil are usually the first to be affected. The symptoms are yellowish-brown spots which later fuse. The leaves then become brown and dry. The infection spreads to younger leaves and follows up to stem. Such heavily affected plants are unable to survive. It often happens, that the stamens dry up even in the closed buds and so do the developing seeds. The characteristic conidia and the septate and branched mycelium could be observed under the microscope on both sides of the infected leaves.
Alternaria brassicae. 1. Conidial chain, 2-3 Germinating conidia, ct conidial tube.
A. brassicae is of common occurrence and a very injurious fungus on Cruciferae. It belongs to the order Moniliales (family Dematiaceae) of Fungi imperfecti. The parasite is transmitted as mycelium or as conidia hibernating in soil, infected plant debris and also on seeds. Humid and warm conditions favour the transmission of the fungus. Chemical methods of controlling the infection are rarely practiced. Some success seems to be attained with spraying the accustomed Cu - preparates or zinc carbamates ("Fuclasin Ultra"-SCHERING). In any case it is necessary to work with sterilized (steamed) soil.
