Roots were taken from potato or whe

Roots were taken from potato or wheat plants grown in field soil in pots in the greenhouse. Approxi- mately 5 g fresh root material from each root system was thoroughly shaken for 20 min at 4‘C in 100 ml sterile 0 1% proteose peptone solution in an Erlenmeyer flask containing quartz particles. Diluted suspensions were plated on tryptic soy agar (TSA), containing 3 g tryptic soy broth (Oxoid) I-‘, supple- mented with 100 mg cycloheximide I-‘, and on King’s medium B (KB) (King et nl., 1954) supplemented with 100 mg cycloheximide, 50 mg ampicillin and 12.5 mg chloramphenicol I-’ (KB’). Colonies were counted after 48 h at ZO’C. Ninety-eight distinct colonies on TSA and 50 on KB+ were selected at random and transferred to TSA- and KB-media supplemented with 4.4g glycine I-’ to screen for cyanide production.