RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM (RFLP) ANALYSIS OF PROGENY FROM AN ALLIUM-FISTULOSUM X ALLIUM-CEPA HYBRID

Allium fistulosum L. (bunching onion) is resistant to many of the impo rtant diseases and pests of Allium cepa L. (bulb onion). Although the first interspecific hybrids were generated more than 50 years ago, the re is no conclusive evidence that any desirable trait in bunching onio n 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 establ ished that the interspecific hybrid and three putative backcross plant s had the cytoplasm of a bunching onion. All 57 random cDNA probes det ected polymorphisms between the bulb and bunching onion for at least o ne of two restriction enzymes. The backcross progenies always possesse d the bulb-onion fragments and an excess of probes detected the bunchi ng-onion fragments. Only one plant showed an acceptable fit to the exp ected 1:1 backcross ratio. Significant deviations from expected segreg ation ratios may be the result of abnormal meiosis in the interspecifi c hybrid. However, these observations could also be explained by a pre viously proposed nuclear-cytoplasmic interaction conditioning preferen tial survival in the bunching-onion cytoplasm of eggs carrying bunchin g-onion chromosomes.