Some observations on the mildew fungus affecting the cucurbitaceous plants

Abstract

Erysiphe cichoracearum DC., Sphaerotheca fuliginea (SCHFECT.) POLL., and Sph. humuli (DC.) BURR. are reported as the powdery mildew fungi attacking cucumber and other members of cultivated cucurbitaceous plants. While in Fukuoka so far observed, Sph. fuliginea is the only cause of the mildew of the cucurbitaceous plants.
The occurrence of perithecial formation of Sph. fuliginea on cucurbitaceous hosts is not uncommon in Fukuoka late in the fall, though it is said difficult to find the perithecia in other districts of Japan.
The mildew fungi (E. cichoracearum and others) obtained from Nicotiana tabacum, Artemisia vulgaris, Sesamum indicum, and Bidens bipinnata are not infectious to cucumber, while the fungus from Arctium lappa (Sph. fuliginea) is pathogenic to cucumber.
Sph. fuliginea from cucumber is infectious to Arctium lappa and Phaseolus radiatus, but is not infectious to Solanum melongena, Chrysanthemum coronarium, Helianthus tuberosum, Hel. annuus, and Nicotiana tabacum.
The difference of resistance due to the difference of ages of the leaves of cucumber against the infection by Sph. fuliginea has been observed. Young leaves which had past 0 to 3 days. before the inoculation, in this experiment, were not affected when examined 5 days after inoculation, and the most susceptible leaves were those which had past 16 to 23 days before the inoculation.