Percent solids and other characteristics of progency resulting from interspecific trisomic onion backcrosses

Segregating populations derived from interspecific trisomic onion backcrosses were evaluated. The trisomic parents were DG 11, DG 33, DG 112 and DG 131. A. cepa ev. 'Temprana' and the interspecific triploid 'Delta Giant' (2n Allium cepa + In Allium fistulosum) from which the above trisomies were derived were also included in this experiment.

Morphological and cytological studies were conducted. Percent solids was determined. Data obtained under field conditions failed to distinguish trisomic from diploid plants. The trisomic backcross populations had higher mean solids content than ev. Temprana' and lower than 'Delta Giant'. Solids from 5.2 to 17.7 percent were found in the segregating populations. The distribution of the solids content of the various populations supports reported research that solids content is quantitatively inherited, therefore selection should be effective in increasing solids. Chromosome counts were made and the extra chromosome was identified in all plants from the backcross population DG 33 and in a group of plants with high solids from the other segregating populations. The transmission rate of the extra chromosome in the backcross population DG 33 was 3.08%. The same extra chromosome belonging to the £. fistulosum genome was present in the four segregating populations. All trisomic plants were found to have high percent solids.

The results suggested that the extra chromosome possesses genes that confer high solids content, which could be incorporated into A. cepa. It was demonstrated that alien addition lines can be used to introgress genes for high percent solids from A^. fistulosum to commercial onion varieties.