Chromosome pairing at different ploidy levels in the tuber-bearing Solanums

Summary

The nature of chromosome pairing at meiosis in some tuberiferous Solanums (2n, 3n and 4n) is described. A number of abnormalities have been noted at meiosis in the diploids including the formation of multivalents and univalents. Although the occurrence of univalents as early as diakinesis suggested that chromosomal differences do exist, the evidence from the diploids as to the nature of the basic genome in Solanum is not clear cut. An examination of meiosis in triploid hybrids (4n × 2n) revealed a considerably higher value for the mean number of bivalents plus trivalents per cell at metaphase I (14.2; 13.5; and 13.3) than has heretofore been reported. The maximum number of such associations recorded was 16. It appears that in the hybrid between the induced tetraploidS. chacoense (n=24) andS. neohawkesii (n=12), at least 8 out of the 12 chromosomes from the diploid parent are capable of exhibiting partial homology. The analysis of pairing in the triple hybrids ((6n × 2n) × 4n) is more complicated. However, there are some indications that autosyndetic pairing within the complement of chromosomes derived from the 4n parent may exist. The occurrence of pairing within the haploid set of chromosomes derived from one diploid species appears to be suggestive of the possible existence of two subgenomes within the haploid genome but further studies of the whole genus are required for a verification of this possibility.