Growth Responses of Tobacco Seedlings in Asep- Tic Culture to Diffusates of Some Common Soil Bacteria '

The conditions that cause the development of symptoms of frenching in tobacco {Nicotiana tabacum L.) plants are unknown. Low nitrogen, ^ low acidity, and excessive moisture ^ have at times been held to be contributing factors. Nevertheless soil from fields of severely frenched plants was often incapable of producing this morphological abnormality in the greenhouse. Abnormal plants transplanted to fresh soil almost always resume normal growth. The disorder is non transmissible. Spencer^ and others have therefore suggested that a labile organic substance (toxin) sometimes present in soils may be the causative agent in this disease. Bacterial interrelations as revealed through studies with antibiotics seem to indicate the possibility that similar diffusâtes capable of a direct action on plants may also accumulate in soil under certain conditions. Data published by the writer ^ ^ afford direct evidence that low concentrations of an organic substance, the amino acid dlisoleucine, in contact with the roots of tobacco seedlings in aseptic cultures may bring about morphological abnormalities resembling those of frenching. The present studies were therefore undertaken to determine whether any of the more common species of soil bacteria form diffusâtes capable of causing abnormal alterations in gross morphology of tobacco plants. The seedlings were aseptically grown in a constant environment. The growth medium selected was a slightly acid mineral agar containing a trace of Bacto-peptone. With or without sucrose