Relationship of Numbers of Zoospores of Phytophthora cryptogea to Infection and Mortality of Watercress

Abstract

Suspensions of motile zoospores were added to individual, 2 wk old watercress [Nasturtium officinale] plants growing in flooded vermiculite. Percentages of infection after 7 days at 25.degree. C in a growth room were 18, 26, 46, 56, 65, 81 and 100 at 50, 100, 200, 300, 500, 103 and 104 zoospores/plant. After 21 days percentages of dead plants were 30, 51, 67 and 81 at 103, 104 105 and 106 zoospores/plant.