An isolate of P. ultimum was obtained from Dr. James Traquair,
Agriculture and Agri-Food Canada, London, Ontario. The culture
was maintained on potato dextrose agar (PDA) medium. Its inoculum
was prepared as described previously (Elmer 2002). In brief,
50 g of pearl millet seeds were placed in 100 mL of H2O in a 500 mL
flask and were sterilized by autoclaving for 1 h on2consecutive days.
Flasks were inoculated with 5-mm-diameter plugs (10–15 plugs) obtained
from the edge of the freshly growing P. ultimum colonies on
PDA medium, and kept in an incubator at 24 °C for 14 days. Various
quantities of the pearl millet inoculum were added to peat
mix in preliminary growth-room experiments to determine the
amounts required to give more than 80% disease incidence within
2 weeks after sowing cucumber seeds.