Author(s): Herman J van Eck, M Y Adillah Tan, Richard GF Visser, Ronald C B Hutten
Despite efforts to control late blight in potatoes by introducing R pi -genes from wild species into cultivated potato, there are still concerns regarding the durability and level of resistance. Pyramiding R pi -genes can be a solution to increase both durability and level of resistance. In this study, two resistance genes, R Pi-mcd1 and R Pi-ber, introgressed from the wild tuber-bearing potato species Solanum microdontum and S. berthaultii were combined in a diploid S. tuberosum population. Individual genotypes from this population were classified after four groups, carrying no R pi -gene, with only R Pi-mcd1, with only R Pi-ber, and a group with the pyramided R Pi-mcd1 and R Pi-ber by means of tightly linked molecular markers. The levels of resistance between the groups were compared in a field experiment in 2007. The group with R Pi-mcd1 showed a significant delay to reach 50% infection of the leaf area of 3 days. The group with R Pi-ber showed a delay of 3 weeks. The resistance level in the pyramid group suggested an additive effect of R Pi-mcd1 with R Pi-ber. This suggests that potato breeding can benefit from combining individual R pi -genes, irrespective of the weak effect of R Pi-mcd1 or the strong effect of R Pi-ber.