INTERSPECIFIC ANEUPLOIDS IN THE GENUS SOLANUM

Abstract

Among 143 progeny from interspecific triploid-diploid crosses in Solanum 67.1% were aneuploid. A study of these aneuploids led to the conclusion that the morphological detection of Solanum trisomics is impossible, even after repeated backcrossing, probably because of the highly heterozygous nature of the material. Unique phenotypic characteristics caused by the presence of the extra chromosome are masked by normal genetic segregation. The lack of distinctive phenotypes makes the establishment of a complete set of trisomics more difficult and complicates efforts to determine the transmission frequency of the extra chromosome. In addition the identification of the extra chromosome in each trisomic will require pachytene analysis. Cytological data were obtained for 39 clones. Although some clones exhibited a few cytological abnormalities, meiosis of the trisomics were basically normal. The metaphase I associations were found in the following frequencies: 1) 11 bivalents and 1 trivalent 29%; 2) 11 bivalents and 3 univalents 11.9%; 3) 12 bivalents and 1 univalent 59.1%. There was no obvious pattern of frequencies within a family, and frequencies with which the univalents moved on or off the plate varied from clone to clone. The extra chromosome was identified for three trisomic clones. The aneuploids were generally quite vigorous and fertile. As expected, male and female fertility decreased as the chromosome number increased but factors other than extra chromosomal inbalance affected fertility.