The use of the topiary gene in adapting Solanum germplasm for potato improvement

Summary

The topiary gene, a single recessive conditioning very short stolons and early tuber initiation, may provide a tool for selecting wild species for tuberization. Topiary segregants may be recognized at the seedling stage, and there is good expression in interspecific hybrids. A genetically diverse diploid population, composed of accessions of 22 species selected for disease resistance and 2n gametes and crossed with sources of the topiary gene, is being developed. Recurrent phenotypic selection for yield and carliness of tuberization will be facilitated by the topiary trait, insect pollination and the self-incompatibility system. Standard varietal evaluation techniques including yield trials, sequential harvests, and tuber quality assessments can be applied to the population to alter gene frequencies or identify suitable parents for crossing to Tuberosum. Selected clones may be maintained in the field without clonal mixture. The population should retain most of the simply inherited disease resistance characteristics present in the original introductions. Adapted germplasm produced by this method should be especially valuable where the number of backcrosses to Tuberosum is to be minimized, as in the improvement of potatoes for quantitative traits such as yield, polygenic disease resistance, and environmental tolerance. Well-adapted clones may contribute a maximum input of genetic diversity through hybridization with Tuberosum haploids and subsequent polyploidization via 2n gametes.