MULTIPLE ALLELES FOR TUBER SHAPE IN DIPLOID POTATO DETECTED BY QUALITATIVE AND QUANTITATIVE GENETIC-ANALYSIS USING RFLPS

Tuber shape in potato is commonly regarded as displaying continuous va riation, yet at the diploid level phenotypes can be discerned visually , having round or long tubers. Inheritance of qualitative tuber shape can be explained by a single locus Ro, round being dominant to long. W ith restriction fragment length polymorphisms (RFLPs) the Ro locus was mapped on chromosome 10. Tuber shape was also studied as a quantitati ve trait, using the length/width ratio as trait value. The estimated b road sense heritability was h(2) = 0.80. The morphologically mapped Po locus explained 75% of the genetic variation, indicating the presence of a major quantitative trait locus (QTL) at the Ro locus and minor g enetic factors. RFLP alleles linked with Ro alleles were used to divid e the progeny into four genotypic classes: Ro female Ro male:Ro female ro:roRo male:roro = 1:1:1:1. The recessive ro allele is identical by descent in both parents. The significantly different effects (P = 0.01 57) of the non-identical alleles Ro female and Ro male provided eviden ce for multiallelism at the Ro locus. Linkage mapping of the Po locus was compared with QTL mapping. Only those markers which are polymorphi c in both parents allow accurate QTL mapping when genetic factors segr egate from both parents. This finding applies to QTL mapping in all ou t-breeders without homozygous inbred strains.