Production of a fungistat and the role of fungi during germination of Digitalis purpurea L. cv. Gloxiniaflora seeds

The seed coats of Digitalis purpurea L. cv. Gloxiniaflora were cultured for indigenous fungi. Alternaria alternata (Fries) was identified as the sole fungus on seeds freshly harvested from unopened capsules, whereas A. alternata, Rhizopus arrhizus (Fischer), Penicillium sp. and other fungi appeared on stored seeds. The appearance of fungi in seed cultures was seasonal, being more frequent in winter and early spring than in summer and autumn. Alternaria grew well on autoclaved seeds, on dehiscent seed coats, or on seed coats separated from the embryos of ungerminated seeds. Rhizopus did not grow on these but grew weakly on the culture medium from viable seeds. A. alternata appears to function as a degradation agent for the seed coat subsequent to germination. Neither fungus was found to be essential to germination of Digitalis seeds. Bioassay of the culture medium from germinating seeds showed that a fungistat effective against both Alternaria and Rhizopus is produced coincident with germination. Based on chromatographic analysis, the fungistat appears to be a cardenolide.