Induction of systemic resistance in potato (Solanum tuberosum L.) plants to late blight by local treatment withPhytophthora infestans (Mont.) de Bary,Phytophthora cryptogea Pethyb. & laff. or dipotassium phosphate

Summary Induced systemic resistance to late blight was found in the potato cultivar Bintje which has no major or minor resistance genes to late blight. The prerequisite was a local inoculation with 5×10³ zoospores/mo, ofPhytophthora infestans race 1, 3, 4, 7, 8, a local inoculation with 2×10³ zoospores/ml ofPhytophthora cryptogea isolated from wheat or local treatment with 50–100 mM solution of K₂HPO₄. Potato plants used in the experiments were propagated in vitro from nodal cuttings. Protection caused by the different inductions was 30 to 70% (assessed as a reduced number of lesions/plant and reduced necrotic tissue/leaf or plant) and tended to positively influence yield and dry matter of the haulm. The induced protection in the potato plant was better in young developing leaves than in fully expanded leaves.