MALE-FERTILITY AND CYTOLOGY OF TRIPLOID HYBRIDS BETWEEN TETRAPLOID SOLANUM-COMMERSONII (2N=4X=48, 2EBN) AND PHUREJA-TUBEROSUM HAPLOID HYBRIDS (2N=2X=24, 2EBN)

Solanum commersonii Dun. is a diploid (2n = 2x = 24, 1EBN) wild specie s of potential value for potato breeding. It is a reproductively isola ted species and cannot be crossed with Tuberosum haploids (2n = 2x = 2 4, 2EBN) or other diploid 2EBN Solanum species. In order to overcome t he EBN barriers, triploid hybrids were produced between Phureja-Tubero sum haploid hybrids, which form 2n pollen grains by parallel spindles, and tetraploid S. commersonii. Microsporogenesis analysis of the trip loids indicated a trend towards low values of chromosome distribution at Anaphase I; lagging chromosomes were often observed as well. Despit e these abnormalities, the percentage of stainable pollen was very hig h, ranging from 5.0% to 74.3%. A high variation in pollen grain diamet er was also evident. Parallel and tripolar orientation of spindles at Metaphase II of microsporogenesis was a common feature of all the trip loids analyzed, but dyads and triads were observed at a very low frequ ency. Therefore, also the frequency of 2n pollen was very low; the dif ferent size of stainable pollen appears to represent the ploidy levels which are possible according to the distribution of chromosomes in An aphase I. The results obtained also suggest that S. commersonii could have minor genes acting at the end of meiosis in such a way that, desp ite the presence of parallel/tripolar spindles, dyads/triads are not f ormed.