ABSTRACTSeveral lipid components from teliospores of the dwarf bunt fungus,Tilletia controversa, inhibited teliospore germination and sporidial formation in the common bunt fungus,Tilletia caries.A crude fatty acid mixture and a purified linoleic acid preparation appeared to be the most inhibitory components in the extracts obtained from the spores ofT. controversa.Inhibition of teliospore germination by crude fatty acid preparations increased after they were treated with lipoxidase. Both the nature and degree of inhibition of spore germination and sporidial formation by pure linoleic acid were similar to that caused by the linoleic acid purified from extracts ofT. controversa.Linoleic acid changed chemically under the bioassay conditions to yield several other substances that were probably oxidation products of the unsaturated fatty acid. Of the 12 pure fatty acids tested, polyunsaturated fatty acids were the most inhibitory. Exogenous lipids occur in bunt balls ofT. controversaandT. caries, mainly as triglycerides with some free fatty acids present. These exogenous triglycerides were 64% linoleic acid, but were only slightly inhibitory even when treated with lipoxidase; however, after the triglycerides were treated with lipase to release free fatty acids, the inhibition of the reaction products increased dramatically. The exogenous lipids were more abundant on spores ofT. controversathan onT. cariesspores, and they may play an important role in extending the germination time of aT. controversaspore population in the field.