GERMPLASM TRANSFER FROM THE WILD TETRAPLOID SPECIES SOLANUM-ACAULE BITT TO THE CULTIVATED POTATO, SOLANUM-TUBEROSUM L USING 2N EGGS

Solanum acaule Bitt. (acl1, 2n=4x=48 and 2n=6x=72) is a wild potato species in which resistance to adverse biotic and abiotic agents has been found. The tetraploid subspecies acaule and aemulans cannot be easily crossed with the common potato, S. tuberosum L. Group tuberosum (tbr, 2n=4x=48) because the development of the endosperm in the hybrid seed is abnormal. Since 4x acl behaves as a diploid in intra and interploidy crosses, it was postulated that the hybridization barrier with tbr could be overcome if the wild species produced 2n gametes. One hundred and ninety-seven plants of 4x acl (22 introductions) were screened for pollen of heterogeneous size; only two plants produced this type of pollen, with 3% and 5% of pollen in the large class, respectively. On the other hand, 427 plants (47 introductions) were screened for 2n eggs through controlled crosses with tbr. Forty-one plants (13 introductions) produced 219 berries of which 46 contained at least one plump seed. Seed from berries with low seed set gave rise to hexaploid hybrids possibly through the functioning of 2n eggs from 4x acl. A sample of these hybrids was successfully backcrossed as female parents to tbr, giving rise to 5x BC1 progenies. These BC1 progenies could be easily back-crossed to tbr, yielding tetraploid or near tetraploid BC2 plants. © 1990 Springer.