1978 Volume 44 Issue 5 Pages 612-618
The inoculation experiments and morphological observations were made to clarify the physiological specialization of Sphaerotheca fuliginea parasitic on Cucurbitaceous plants, eggplant, edible burdock and Japanese butterbur. The inoculation experiments of the fungi parasitic on melon, cucumber, winter squash and bottle gourd onto nineteen host plants of S. fuliginea showed that these isolates were similar in their host ranges. Mamely, melon, cucumber, winter squash and bottle gourd became infected easily by the fungi, but watermelon and white gourd belonging to the same family, Cucurbitaceae, were not infected. Helianthus annuus, Cosmos bipinnatus, Zinnia elegans of the Compositae and Impatiens balsamina of the Balsaminaceae were also infected by these isolates. The fungus on watermelon had nearly similar host ranges to that parasitic on melon. Water melon fungus, however, was more virulent on watermelon than melon fungus. Fungi which were parasitic on eggplant, edible burdock and Japanese butterbur were virulent only on their respective original host plants. Morphological observations showed that the length of the conidia of the fungus parasitic on eggplant was somewhat longer than that of the fungus parasitic on melon, and that any other remarkable difference was not found among the fungi parasitic on other plants. Five specialized forms of S. fuliginea were recognized according to their host ranges. They are: (1) Fungus parasitic on Cucurbitaceae, except watermelon and white gourd; (2) fungus parasitic on watermelon; (3) fungus parasitic on eggplant; (4) fungus parasitic on edible burdock and (5) fungus parasitic on Japanese butterbur. Each of the above-mentioned fungi can be regarded as a specialized form of S. fuliginea.