hibition of root cell energy metabo

hibition of root cell energy metabolism is suggested to be responsible for potato yield reductions in short potato-rotation soils. Hydrogen cyanide is the microbial metabolite possibly involved in inhibition of energy metabolism. This is supported by the following observations: (1) approximately 50% of potato rhizosphere pseudomonads was shown to produce cyanide in t&o; (2) 5 pt.+ HCN inhibited cytochrome oxidase respiration by at least 40% in intact potato roots in cifro; (3) cyanide pr~uction in cirro by Pseudorn~ff~ sp. isolate WCS361 depended on the Fe’+ concentration of the medium. Growth promoting fluorescent P~e~~~~~~~ spp isolates WCS374 and WCS358 did not produce cyanide in rim. A hypothesis. that potato plant growth is depressed in short potato rotation soils by the microbial production of cyanide in the rhizosphere is discussed. In such soils. bacteria producing specific siderophores increase growth by competing with cyanide-producing organisms for Fe’+.