VARIABILITY FOR RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS (RFLPS) ANDRELATIONSHIPS AMONG ELITE COMMERCIAL INBRED AND VIRTUAL HYBRID ONION POPULATIONS

Nuclear RFLPs were used to estimate relationships among 14 elite comme rcial inbreds of bulb onion (Allium ct pa) from Holland, Japan, and th e United States. Variability for known alleles at 75 RFLP loci and 194 polymorphic fragments revealed by 69 anonymous cDNA probes and a clon e of alliinase were scored to yield genetically characterized and unch aracterized data sets, respectively. The inbred onion populations poss essed more than two alleles at 20 of 43 (46%) codominant RFLP loci. Re lationships among the inbreds were estimated by cluster analysis of si mple-matching (genetically characterized data) and Jaccard (geneticall y uncharacterized data) coefficients using the unweighted pair group m ethod and agreed with known pedigrees. RFLPs confidently distinguished among elite inbreds within and between specific market classes. RFLP profiles for virtual hybrids were computer-generated by combining game tic arrays among inbreds of the same market class and analyzed as desc ribed above. Allelic and genetically uncharacterized RFLPs confidently distinguished among these hybrids, even though heterozygosity for man y markers produced a majority of monomorphic fragments. We randomly sa mpled decreasing numbers of RFLPs from the complete data sets and calc ulated simple-matching and Jaccard distances, noting the numbers of pr obes that were unable to distinguish any two inbreds or hybrids. As fe w as 10 polymorphic probe-enzyme combinations distinguished among all the inbreds and samples of 20 genetically characterized or 10 genetica lly uncharacterized clones distinguished all the virtual hybrids. This study demonstrated that the previously reported few RFLPs observed am ong open-pollinated (OP) onion populations were due to the highly hete rozygous nature of the OP population.