Some Water Relations of Erysiphe Polygoni Conidia

Abstract

The distinctive morphological characters of the conidia of Erysiphe polygoni are their large size, fragility, large vacuoles, thin walls, and the active Brownian movement of particles in the protoplasm and vacuoles. The weight, volume, and surface area per spore were determined as 792 × 10^-11 grams, 728 — 10^-11 cm.³, and 191 — 10^-7 cm.² respectively. The density of conidia of E. polygoni was measured by their rise or fall in solutions of known density, by their rate of fall in water, and by the relation between volume and weight of a measured mass of spores. The average value was 1.094. The density of Uromyces phaseoli uredospores and Peronospora destructor sporangia was determined as 1.36 and 1.34 respectively. The moisture content of E. polygoni conidia was determined as 72 percent by the conventional oven dry weight method and 53 to 74 percent by the heat of solution of the spores in sulfuric acid. A high water content might also be indicated by their low specific gravity and their lack of shrinkage in a humid atmosphere. In a laboratory environment where a free water surface lost water at about 800 mg./hr./dcm.², conidia of E. polygoni lost water initially at about 0.640 mg./hr./dcm.², or spores lost water at about 0.08 percent of the rate from a free water surface. This indicates an efficient mechanism of water retention of the spores. Germination continued even after the mass of the spores had lost 72 percent of its water content at 20 hours after seeding. Water loss from spores rose to a maximum rate at about 8 hours after seeding and fell to zero at about 72 hours after seeding. A 10,000 percent increase in the amount of spores per unit area caused only a 32 percent decrease in the rate of water loss per spore. The relative rate of water loss from germinated and non-germinated spores was determined by comparing the weight loss of a spore sample in green light showing a high percentage of germination with the weight loss of a spore sample in darkness showing a low percentage of germination. Germinating spores lost 85 percent more weight than non-germinating spores in 7 hours. The relative rate of shrinkage of germinating and non-germinating spores was determined by measuring microscopically and at intervals the diameter of individual spores some of which germinated and some of which did not. Germinating spores decreased in volume at about 3 times the rate of non-germinating spores.