The genetic basis for tolerance to Aphanomyces root rot found in a selection of P.I. 175227 was studied in a greenhouse tank test. Parental, F1, BC, F2, and F3 populations were screened by subjecting the seedlings to a pure culture of the pathogen.
The results showed that tolerance was associated with dominant, “wild-type”, alleles at 3 unlinked marker loci (Le, A, Pl) and that substitution of the recessive, horticulturally desirable, allele at each of these loci led to a decrease in tolerance. The demonstrated associations were ascribed to genetic linkage rather than to pleiotropy.