Pseudomonas putida strain BK8661, which produces siderophore(s), antibiotic(s), and low levels of hydrogen cyanide (HCN), suppresses growth of Septoria tritici and Puccinia recondita f. sp. tritici in vitro and on wheat leaves, Pleiotropic mutants of strain BK8661 deficient in siderophore and antibiotic synthesis were significantly less effective in suppressing symptoms than was the wild type, HCN overproducing derivatives of the pleiotropic mutants were constructed by the integration of the hcnABC gene cluster from Pseudomons fluorescens CHA0, In the absence of siderophore(s) and antibiotic(s), HCN production by the overproducing bacterial strains resulted in a small but statistically significant increase in the suppression of symptoms caused by S. tritici and P. recondita f. sp. tritici on wheat seedling leaves.