Morphological and molecular tracking of Allium fistulosum L. introgressed into A. ceps L.
Interspecific hybridization is a possible way to introduce desirable traits from Allium fistulosum L into Allium cepa L. to improve A. cepa onion cultivars. However, onion cultivars possessing A. fistulosum genes have not been released. Sterility of F1 hybrids and their derivatives has been a major barrier for successful introgression. This dissertation reports the recovery of A. cepa type onions with A. fistulosum genes. F1BC3 plants have been generated by backcrossing A. cepa to A. cepa x A. fistulosum hybrids. F1BC3 plants were evaluated for morphology, fertility, pink root incidence, soluble solids content (SSC), pungency, isozymes, chromosome morphology, and genome recombination by fluorescence in situ hybridization (FISH). Recombinant F1BC3 plants were identified by exhibition of both A. cepa and A. fistulosum isozyme alleles and by plant morphology. Growth habit and floral characters of the F1BC3 plants were much like A. cepa. SSC and pungency in the F1BC3 bulbs ranged from low as in A. cepa to high as in A. fistulosum. Recombinant bulb-type onions with high SSC and low pungency were identified. Fertile F1BC3 plants with high pollen viability and which set seeds were recovered. Polyacrylamide gel electrophoresis detected 12 esterase bands in A. cepa and A. fistulosum. These bands were assigned to 4 zones according to migration distance, a- and p-substrates, and banding patterns of hybrid derivatives. Six of 51 F1BC3 plants were identified with A. fistulosum esterase alleles. Esterases were more polymorphic than single-locus isozymes in Allium. Genomic in situ hybridization of A. cepa and A. fistulosum was done with biotin-labeled genomic DNAs of both species. A highly repetitive 376 bp A. fistulosum DNA sequence revealed telomeric hybridization sites; similar telomeric sites were observed when hybridizing labeled A. fistulosum genomic DNA onto A. fistulosum chromosomes. In situ hybridization patterns identified recombinant chromosomes in F1BC3 plants. FISH provided visual evidence that A. fistulosum DNA has been introgressed into the A. cepa genome. Recombinant fertile plants make possible the continued application of interspecific breeding for A. cepa improvement.