Relationships between establishment of Erysiphe cruciferarum and soluble amino‐acids in leaves of Brussels sprouts

The ability of Erysiphe cruciferarum to establish infections on detached foliage and button leaves of two F l cultivars of Brussels sprouts grown in the field was examined under standard conditions. Consistently more infections developed on Goldmine than on Ulysses. On foliage leaves of both cultivars the numbers of infections fluctuated from week to week but generally increased with time on samples taken from September to December. On Goldmine, more infections developed on the oldest foliage leaves than on those of intermediate position on the stem and only infections on the mature leaves sporulated well. The number of infections increased progressively on leaves further into the sprout buttons of both cultivars. Fungal establishment on foliage and button leaves of Goldmine was related to the amino‐acid content of comparable uninoculated leaves.