Observations on the Mode of Infection of Lucerne Roots by Phytophthora megasperma

Abstract

Infection of roots of resistant and susceptible lucerne cultivars by zoospores of Phytophthora megasperma var. sojae was studied in solution culture. Zoospores accumulated, encysted, germinated and penetrated roots at two different regions, the region of cell division and cell extension at the root apex and at the junction of a lateral root with the tap-root. Zoospores exhibited similar tactic responses to both resistant and susceptible cultivars. The infection by zoospores a t root junctions is a possible explanation for tap-root lesions consistently originating at the junction of the tap-root with a lateral root on plants infected in the field.