Allium fistulosum L. (bunching onion) is resistant to many of the important diseases and pests of Allium cepa L. (bulb onion). Although the first interspecific hybrids were generated more than 50 years ago, there is no conclusive evidence that any desirable trait in bunching onion has been successfully transferred to bulb onion by backcrossing. We identified RFLPs in the chloroplast and nuclear genomes to assess DNA transfer from bunching to bulb onion by backcrossing an interspecific hybrid to a bulb onion. Polymorphisms in the chloroplast genome established that the interspecific hybrid and three putative backcross plants had the cytoplasm of a bunching onion. All 57 random cDNA probes detected polymorphisms between the bulb and bunching onion for at least one of two restriction enzymes. The backcross progenies always possessed the bulb-onion fragments and an excess of probes detected the bunching-onion fragments. Only one plant showed an acceptable fit to the expected 1:1 backcross ratio. Significant deviations from expected segregation ratios may be the result of abnormal meiosis in the interspecific hybrid. However, these observations could also be explained by a previously proposed nuclear-cytoplasmic interaction conditioning preferential survival in the bunching-onion cytoplasm of eggs carrying bunching-onion chromosomes.
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