Heritability of clover rot resistance (Sclerotinia spp.) in red clover (Trifolium pratense) populations

European red clover (Trifolium pratense) crops are susceptible to clover rot, a destructive disease caused by Sclerotinia trifoliorum or S. sclerotiorum. The lack of knowledge on the heritability of clover rot resistance is, among other reasons, responsible for the slow progress of resistance breeding. In this paper, we acquired insight in the heritability of clover rot resistance through divergent selection by our high-throughput bio-test on an experimental diploid population. The disease susceptibility indices of the first generation after selection for susceptibility and the first and the second generation after selection for resistance were compared with the susceptibility of the original population. The susceptible population (79.2%), the original population (70.5%) and the first generation resistant population (62.3%) differed significantly in susceptibility (p < 0.001). The first (62.3%) and second generation resistant population (60.0%) did not differ significantly in susceptibility. The heritability (h2) of clover rot resistance was low: 0.34 and 0.07 in the first and second cycle of selection respectively. This indicates that mass selection is not suitable to improve clover rot resistance. Family selection may allow a sustained increase in resistance for multiple generations.