Associations among 45 hybrids widely grown in the U.S.; comparisons of groupings shown by isozymic versus RFLP data

--J.S.C. Smith, B.A. Orman, S. Wall

Forty-five widely grown proprietary named hybrids released from a total of 8 organizations were profiled for 19 isozymic loci and also by 80 RFLP probes well dispersed through the maize genome. Modified Rogers' Distances were calculated between all pairs of hybrids from the isozymic data; distances from RFLP data were computed according to Nei and Li (1979). Associations among hybrids were revealed by cluster analysis performed upon each of the respective distance matrices. Correlation of distances between hybrids for isozymic versus RFLP data was r = 0.70. Isozymic data placed 17 hybrids into 5 groups within which hybrids had indistinguishable profiles. Twenty-eight (62%) of hybrids had unique isozymic profiles. All hybrids had unique RFLP profiles. However, some distances, on the basis of RFLP data, were small and RFLPs confirmed the associations for 11 of 13 hybrids into 3 groups that were previously shown by isozymic data. Within each of these groups, hybrids shared more than 95% of RFLP variants. There were no examples of hybrids with different isozymic profiles yet with similar RFLP profiles. Isozymic data could provide a relatively cost effective and timely screen for hybrids with either similar, or different germplasm constitutions. Additional and more detailed analyses to test for similarities among hybrids or to show associations among hybrids should utilize data from additional genetic sites that will more completely sample the genome. Knowledge of the frequencies of occurrence of bands across lines or hybrids can allow calculations of match probabilities to be calculated. Data from relatively few probes might be sufficient to show very long odds that a matched profile could have been independently derived. As the frequencies of the bands across a relevant set of germplasm decreases, the numbers of probes needed to indicate long odds will also decrease. Such data can be provided by RFLPs.

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