Induction of systemic resistance to rust in Vicia faba by phosphate and EDTA: effects of calcium

Resistance in the upper leaves of broad bean ( Vicia faba ) plants to infection by the rust fungus, Uromyces viciae‐fabae, was increased following treatment of the lower leaves with 10 m m potassium phosphate or 5 m m EDTA. Increasing the interval between treatment of the lower leaves and inoculation of the upper leaves had little effect on rust infection. Thus rust infection was reduced by 50 and 34% if the upper leaves were inoculated 1 day after treatment of the lower leaves with potassium phosphate or EDTA, respectively, while there was a 75% reduction in infection if the interval between treatment and inoculation was increased to 12 days. Application of calcium nitrate (10 m m ) after the phosphate or EDTA treatments prevented the induction of systemic resistance. Calcium nitrate applied alone to the lower leaves had no significant effect on rust infection of the upper leaves.