INHIBITION OF HYPOXYLON PRUINATUM (KLOTZSCHE) CKE. BY ASPEN BARK MEAL AND THE NATURE OF ACTIVE EXTRACTIVES

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Abstract
The inhibitory power of poplar bark against the growth of Hypoxylon pruinatum (Klotzsche) Cke. was demonstrated on autoclaved bark meal agar. Activity varied with the species, time of cutting, and locality, but was highest in the bark of Populus tremuloides Michx. Maximum activity occurred in the roots and decreased towards the top of the tree. Neutral, basic, and acid fractions obtained from active ethyl acetate extracts of aspen bark showed seasonal quantitative variations which were characteristic for each fraction and for the part of the tree sampled. The acid fraction contained three active compounds: pyrocatechol, an undetermined phenol, and a glycoside (R). The neutral fraction contained an active glycoside (W). Glycoside (R) was mainly concentrated in the lower stem and glycoside (W) in the upper stem. The concentration of the two glycosides in the bark varied with locality. The influences of pH, temperature, and different chemicals on the fungistatic action of pyrocatechol were investigated to elucidate their rôle in disease resistance. In wilting tests, poplar leaves showed a light necrosis at 1320 p.p.m. of pyrocatechol, whereas 165 p.p.m. were lethal to tomato plants.