Germplasm enhancement with potato haploids

Haploid-species hybrids were produced from crosses between 40 Solanum tuberosum Group Tuberosum haploids (2n= 2x = 24) as females and wild 2n = 2x = 24 Solanum species S. berthaultii, S. bollviense, S. canasense, S. infundibuliforme, S. microdontum, S. raphanifolium, S. sanctee-rosae, and S. tarijense as males. Several important results were obtained: variation for tuberization in the hybrids was striking and discrete, with plants that did not tuberize adjacent to full sibs with large, smooth tubers; tuber yield in some hybrids significantly exceeded that of the parents—1.5 kg/hill compared to 0.5 kg/hill in the haploid parents and no tubers produced by the species parents; haploids derived from the same tetraploid parent differed greatly in their ability to produce hybrid families with good tuberization; the species parents also influenced tuberization in hybrid progeny—the particular genotypes of S. berthaultii and S. tarijense were the best species parents. Wild potato species contain valuable traits and the allelic diversity necessary to increase heterozygosity, but they do not tuberize in the North Temperate region. Therefore, hybridization with haploids is a valuable method of putting this germplasm into a form that tuberizes, for ease of evaluation and maintenance. Haptoid-species hybrids that produce 2n gametes provide the basis for an effective method of transferring germplasm from the 2x level to tetraploid cultivars. They also provide the essential materials for breeding schemes involving the production of 4x progeny from 4x × 2x or 2x × 2x crosses.