Studies on the Growth Inhibitory Substances Contained in Tulip Plant against Phytophthora spp: The seasonal change of inhibitive effectiveness of the tissue decoction on the growth of Phytophthora porri Foister

It has been reported by Bergman and Schoenbeck that several antibiotic substances, such as tuliparin, are present in the tulip plant, especially in the stigma of the pistil. In this paper, using the crude extracts obtained by tissue decoction and their antibiotic spectra, the difference in antibiotic contents among several tulip varieties and the occurrence of the active substances over the period ofa year were studied. As shown by inoculation tests, Phytophthora porri invades the tulip bulb through the young bud but not through the scaly leaf. The root is infected but the hyphae hardly develop as far as the bulb through the root plane. On medium made from the bulb decoction, Botrytis cinerea grew well, but P. porri, P. citrophthora, P. capsici, and P. melonis were inhibited their growth. These inhibitory actions of the decoction for Phytophthora are also shown by the bulb decoction media of garlic and lily, but not those,of onion and hyacinth within the Liliaceae. There are few differences in the contents of the inhibitory substances among three tulip varieties, Maureen, Flying Dutchman, and The Bishop. Inhibitory action of the decoction decreased while the bulbs were stored at comparatively high temperatures (35°C, 45°C). When the bulbs were planted in early winter, the contents of active substances in the bulb are not so great. Nor does the content of active substance increase with the emergence of buds from the bulb through the soil. When the new leaves are elongated and their assimilation ability becomes active, the active substance increased gradually in the leaves. At the time when the new bulbs increase in size, the substances synthesized in the leaves moved to the new bulb in early spring and then disappeared in the leaves with their senescence. Therefore, it can be concluded that the infection of P. porri in tulip plants is accomplished while the sprouts are emerging through soil, before the active substance appear to inhibit the fungus invasion.