QTL ANALYSIS OF POTATO TUBERIZATION

Quantitative trait loci (QTLs) affecting tuberization were detected in reciprocal backcrosses between Solanum tuberosum and S. berthaultii. Linkage analyses were performed between traits and RFLP alleles segreg ating from both the hybrid and the recurrent parent using a set of fra mework markers from the potato map. Eleven distinct loci on seven chro mosomes were associated with variation in tuberization. Most of the lo ci had small effects, but a QTL explaining 27% of the variance was fou nd on chromosome 5. More QTLs were detected while following alleles se gregating from the recurrent S. tuberosum parent used to make the back cross than were detected by following alleles segregating from the hyb rid parent. More than half of the alleles favoring tuberization were a t least partly dominant. Tuberization was favored by an allele from S. berthaultii at 3 of the 5 QTLs detected by segregation from the hybri d parent. The additive effects of the QTLs for tuberization explained up to 53% of the phenotypic variance, and inclusion of epistatic effec ts increased this figure to 60%. The most common form of epistasis was that in which presence of an allele at each of 2 loci favoring tuberi zation was no more effective than the presence of a favorable allele a t 1 of the 2 loci. The QTLs detected for tuberization traits are discu ssed in relationship to those previously detected for trichome-mediate d insect resistance derived from the unadapted wild species.