Pre-selection for Phytophthora cactorum (Leb. &Cohn) Sehroet. resistance in apple seedlings

Inoculation of apple seedlings at the two-leaf stage with a Phytophthora cactorum zoospore suspension provided a rapid method of pre-selecting for collar rot resistance, since the susceptible plants died within 2 weeks of inoculation while the resistant plants continued to grow satisfactorily. The presence of the resistance gene Pc was not alone sufficient to explain the observed segregation.