Comparison of sexual and somatic interspecific hybridization in {lcub}it Brassica/{rcub}

Brassica napus, a natural allotetraploid between B. rapa and B. oleracea, has been resynthesized via sexual and somatic interspecific hybridization to make a direct comparison of these two hybridization systems as to their utility in an applied plant breeding program. Intersubspecific hybrids of each parent were used to enhance the limited germplasm of vegetable B. napus. In theory, such parents should result in morphologically uniform, allotetraploid somatic hybrids but morphologically variable, allodiploid sexual hybrids. Direct comparisons have not been made to test this hypothesis.; Seventy-two somatic hybrids were produced in two protoplast fusion experiments as confirmed by isozyme markers. Most hybrids exhibited a rosette form with green, pubescent foliage and a DNA content indicating allotetraploid status. The remaining hybrids were caulescent, with foliage that was rugose, blue-green, near-glabrous, and waxy, inflorescences were often irregular and plants were chimeric for flower color (white and yellow); these plants were of higher ploidy levels. Organelle-specific RFLP probes indicated a non-random segregation of organelles greatly favoring those of B. rapa; many hybrids had mitochondrial DNA markers from each parent indicating rearrangement or recombination. Allotetraploid hybrids had high ({dollar}>{dollar}90%) pollen viability and high female fertility. Self-incompatibility was found in hybrids derived from only one of the two self-incompatible B. rapa siblings used in the fusions; plants from the other fusion experiment were self fertile. Observations of ca. 700 progeny from three somatic hybrids (R{dollar}sb1{dollar} generation) showed diverse morphological segregation.; Reciprocal sexual crosses between the same parent plants used above yielded F{dollar}sb1{dollar} hybrids from 27 individual embryos. There was considerable variation in morphology and isozyme banding patterns among allodiploid F{dollar}sb1{dollar} hybrids, yet all were pubescent and contained only maternal cytoplasm. Flowers of the sexual hybrids were male sterile. Morphological variation within the F{dollar}sb1{dollar} generation was similar to, but less than, that of the R{dollar}sb1{dollar} population, presumably due to the inherently low interspecific F{dollar}sb1{dollar} population size. These data suggest that when available, somatic hybridization may be the more efficient venue for the plant breeder intending to enhance germplasm variability or to transfer quantitative traits into an allopolyploid crop.