Growth of the Cotton Root-rot Fungus in Synthetic Media, and «the Toxic Effect of Ammonia on the Fungus'

The cotton root-rot disease, caused by the fungus Phymatotrichum omnivorum (Shear) Duggar, has been the subject of extended investigations since its discovery by Pammel {5) ^ in Texas in 1888. Although much knowledge has been obtained in regard to the ecolo^ of the fungus, its life history, morphology, and some of its physiological aspects, there is as yet little known regarding the growth behavior of the pathogène under different conditions of nutrition. Several investigators have reported that the fungus grows well on a variety of media, such as cooked vegetables, various agars, plant decoctions, and sterilized roots or stems of many plants; but few attempts have been made to determine the effect of specific compounds in synthetic media on the growth of the fungus. One exception is the recent work of Ezekiel, Taubenhaus, and Fudge {!), who find that the fungus "grows readily in synthetic media" and is able to utilize both organic and inorganic nitrogen. During the spring of 1931 the writers also studied the growth behavior of the fungus in nutrient solutions, with special attention to the nutrition of the organism with various nitrogen compounds. Comparisons were made of five different inorganic sources of nitrogen. In these studies it was foimd that practically no growth of the fimgus occurred with ammonium nitrate or ammonium sulphate after 11, 18, and 31 days, whereas with calcium, sodiimi, and potassium nitrates growth was abimdant. When this apjparently toxic effect of ammonium salts was observed, other experiments were made to determine the effects of ammonium hydroxide and ammonia on the mycelial and sclerotial stages of the fungus. These experiments and observations form the basis of this paper.