GLYCOALKALOID CONTENT IN TUBERS OF HYBRID AND BACKCROSS POPULATIONS FROM A SOLANUM-TUBEROSUM X S-CHACOENSE CROSS

The glycoalkaloid contents of tubers were measured in hybrid and backcross populations derived from a cross of Solanum chaconseBitter (PI 472810, 2n=2x=24) with Solanum tuberosum L. (2n=4x=48). In tubers sampled from near the median size in each population and parent, the mean total glycoalkaloid (TGA) contents of the S. chacoense and S. tuberosum parent genotypes, and the F-2 and F-4 hybrid genotypes were 245, 4, 39, and 35 mg/100 g fresh weight (fw), respectively. Backcrossing the F-2 genotypes to S. tuberosum reduced the mean TGA content to 15 mg/100 g fw. A second backcross further reduced the content to 9 mg/100 g fw. However, some genotypes in both backcross populations (25% and 10%) had TGA contents above the generally accepted upper limit of 20 mg/100 g fw. Tuber size was significantly smaller in the S. chacoense parent and the hybrid populations compared with the size in the S. tuberosum parent and backcross populations. In a second sampling of tubers from each population, intentionally selected to equalize tuber size among populations, the mean tuber size for populations was reduced by 79%. The mean population TGA content increased by 44%. However, the differences and rankings among parent, hybrid, and backcross populations were the same for both tuber samplings.