Performance of haploid x wild species, 2x hybrids (involving five newly evaluated species) in 4x × 2x families

The 4x × 2x breeding scheme in potato allows introgression of germ-plasm from the 2x wild species into the cultivated tetraploid. Eighteen 4x × 2x, forty-five 4x × 4x, seven 4x-selfs, and five open pollinated (OP) families were transplanted in a randomized complete block design with two replications and 18 plants per family per replication. The 2x parents of the 4x × 2x families were seven haploid x wild species hybrids. These hybrids involve five 2x, wild species,Solanum bukasovii, S. gourlayi, S. muhidissectum, S. vermi, andS. verrucosum, which had not previously been evaluated in the 4x × 2x breeding scheme. Data were recorded for family yield, maturity, tuber uniformity, tuber number, and general tuber appearance. The 4x × 2x families as a group performed as well as or better than the 4x × 4x, 4x-self, and 4x-OP groups for all traits except maturity. Within family maturity distributions for 4x × 2x families indicate the possibility to select early maturing clones from high yielding families. Eleven of the fifteen families in the top 25% of the 4x × 2x and 4x × 4x families for yield were 4x × 2x families. Three of the four 2x parents evaluated for parental performance gave highly significant responses for increased yield. 4x × 2x families with Chiquita as a parent were the poorest yielding while several of the 4x x 4x families of which it was a parent were among the highest yielding: This indicates that the benefits of maximum heterozygosity may be overridden if the percentage of unadapted germplasm is too high.