Two related genotypes of Solanum microdontum carry different segregating alleles for field resistance to Phytophthora infestans

Six F(1) populations produced from crosses between two Solanum microdontum genotypes and three S. tuberosum genotypes have been assessed for resistance to Phytophthora infestans (late blight; LB) in the field and proved to segregate for P. infestans resistance. The six populations were subjected to genetic mapping using AFLP markers in combination with a core map consisting of RFLPs and a few PCR-based markers. The two S. microdontum parents MCD167 and MCD178 harbour different alleles contributing to resistance. In the MCD167 set of populations a major QTL contributing to resistance was located on chromosome 4. This locus was not detected in the MCD178 set of populations. In the latter set of populations, a major QTL for resistance was detected on chromosome 10. This locus for resistance was not detected in the MCD167 set of populations. A third QTL contributing strongly to resistance was detected on chromosome 5. However, this locus was not consistently detected in all populations. For the loci on chromosome 5 and 10, segregation for resistance alleles from the susceptible parents was also observed. The results provide a starting point for future combinations of genes, to predict the value of each combination and finally to obtain potato germplasm carrying high levels of durable resistance to LB.