Accumulation of minor gene resistance to Peronospora trifoliorum in diploid alfalfa

The inheritance of diploid Medicago sativa resistance to Peronospora trifoliorum, because of genes with small, cumulative effects, was studied. (...) The results indicated that high levels of minor gene resistance were derived from plants with no readily apparent resistance without fixing the genes for resistance, and that minor gene resistance generally was not expressed in progeny of a resistant-by-susceptible cross. Hence, the expression of minor gene resistance was dependent on genetic background and may have been masked by epistatic susceptibility