Diurnal Responsiveness of Erysiphe graminis to Nutrients

Abstract
Plates of plain agar and nutrient agar (0.8% agar, 0.6% fructose, and 0.003% animal lecithin) were seeded with conidia of E. graminis from greenhouse barley plants at various times of the day and incubated at 16[degree]C in the dark. Germ tube growth, measured 5 days after seeding, was greatest from seedings made about noon and poorest from seedings made at 8:30 a.m., the former being 85u or 175% greater than the latter. Growth at all times was greater on the nutrient agar than on plain agar, being 40% greater in seedings made at 8:30 a.m., and 236% greater in seedings made at 12:30 p.m. Thus there is a clear-cut diurnal cycle of the influence of nutrients on growth. Germination ranged from 25% to 92%, and showed no diurnal cycle.
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