Translocatable Plant Growth Inhibitors Produced by Penicillium Thomii and Arachniotus trisporus.

The fungus cultures used in these studies were maintained as soil stocks. Conidial suspensions from seven-day-old potato-dextrose-agar slant cultures prepared from soil stocks were used to inoculate 500-ml Erlenmeyer flasks containing 100 ml of corn steepcerelose medium (Staley's corn steep liquor, 40.0 gm; cerelose, 40.0 gm; CaC03, 3.5 gm; NaN03, 3.0 gm; K2HP04, 0.5 gm; MgS04, 0.25 gm; de-ionized H20, 1000 ml). Two drops of Dow Corning Antifoam AF were added to each flask prior to autoclaving. After inoculation the flasks were placed on a reciprocating shaker (99 to 100 cpm with 3-inch strokes) at 27 to 28? C for 7 days. At the end of this time the mycelial growth in each flask was removed by filtering through Whatman No. 1 filter paper and discarded. The culture filtrates were adjusted to pH 5.0 and one drop of ? ween 80 per 100 ml (approx.) of filtrate was added. The undiluted filtrates were frozen until needed. Filtrates from approximately 700 fungi were collected in this manner. Approximately 350 of these were unidentified soil isolates obtained by routine plating-out procedures and 350 were identified as to genus and/or species. In addition, 500 "aetinomycete" culture filtrates obtained from cultures routinely isolated from soil were obtained from the Eli Lilly Company of Indianapolis, Indiana. With two exceptions these filtrates showed no antibiotic activity toward a wide spectrum of microorganisms. The methods used in obtaining these culture filtrates were similar to those described above for the fungus cultures. The shake-flask medium, adjusted to pH 7.0, was as follows: Bacto-peptone, 5.0 gm; glucose, 10.0 gm; molasses (Brer Rabbit Green Label) 20 ml; FeS04 ? 7 H20, 0.01 gm; and distilled water, 1000 ml. The inoculated flasks were placed on a reciprocating shaker (114 cpm with 2-inch strokes) for 5 days at 30? C. As with the fungus cultures the growth in each flask was removed by filtration and discarded. The culture filtrates were treated as described above and frozen until needed.