PHYTOPHTHORA SPP. IN SOILS OF THE OKANAGAN AND SIMILKAMEEN VALLEYS OF BRITISH COLUMBIA

Abstract

Phytophthora cactorum is widely distributed in irrigated soils in the Okanagan and Similkameen valleys of British Columbia. Other species isolated, when over 1800 soil samples were assayed for the presence of Phytophthora fungi, were P. cryptogea twice, P. cambivora once, P. megasperma var. sojae once, and P. drechsleri twice. Phytophthora spp. were not recovered from virgin soils nor from non-irrigated cultivated soils, nor from orchard soils receiving irrigation water that is chlorinated. P. cactorum, P. cryptogea, and P. cambivora are pathogenic to rootlets of pear, cherry, apricot, and peach seedlings. P. megasperma var. sojae and P. drechsleri were weakly to non-pathogenic to these hosts. Pear and apple rootlets exerted a chemotactic effect on zoospores of P. cambivora and P. cactorum.