4. Seed potatoes shall not be certified under Council Directive 66/403/EEC(1) on the marketing of seed potatoes unless they derive in direct line from material certified free of Potato Ring Rot. Such certification shall be based on tests carried out either:
on plants of the initial clonal selection, at least where the contamination affects seed potato production in the country of origin, or
on representative samples of the basic seed potatoes or earlier propagations.
OJ No. L125, 12.7.66, p.2320.