SOME FACTORS AFFECTING GROWTH OF APHANOMYCES EUTEICHES IN SYNTHETIC MEDIA

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Abstract
Papavizas, G. C., and C. B. Davey. (USDA, ARS, Crops Research Division, Beltsville, Maryland.) Some factors affecting growth of Aphanomyces euteiches in synthetic media. Amer. Jour. Bot. 47(9) : 758–765. Illus. 1960.—Some nutritional requirements of 3 single‐zoospore isolates of Aphanomyces euteiches Drechsler were studied in a synthetic medium (SM‐1) consisting of mineral salts, D‐glucose, DL‐glutamic acid, and thioglycolic acid. Micronutrients were essential for growth, whereas vitamins were not. Controlled pH experiments showed that the fungus has a relatively wide pH range (5.2–7.7) for growth with an optimal range between 5.4 and 6.5. When the pH of the medium was maintained within the optimal range by periodic adjustments, ammonium nitrogen was utilized as the sole source of nitrogen. Nitrate nitrogen was unavailable to the fungus under all conditions. DL‐glutamic acid was superior as a nitrogen source to either the D or the L isomer. Growth rate and final mycelial dry weight in a synthetic medium (SM‐2) containing 14 amino acids in proportions found in 1.0% solution of yeast extract approximated those obtained in complex media. Mycelial dry weights in SM‐2 were superior to those obtained in the glucose‐glutamic acid‐thioglycolic acid medium, but this superiority was due to DL‐methionine, a sulfur‐containing compound of the amino acid mixture. Sulfates were not utilized as sole source of sulfur, whereas cysteine, cystine, and thioglycolic acid supported fair amounts of growth. The optimal sulfur concentrations from thioglycolic acid for growth in SM‐1 were between 128 and 192 mg/1. Mycelial yields equalling or exceeding those supported by complex media were obtained with high concentrations of D‐glucose and DL‐glutamic acid.