Associations among inbred lines revealed by RFLP data and correlations with F1 yield and heterosis --J. S. C. Smith, O. S. Smith, S. L. Bowen, R. A. Tenborg, and D. Grant Ten elite inbred lines of maize involving 2 sets of 5 lines, one primarily Iodent and the other mainly Iowa Stiff Stalk Synthetic, with pairs of lines within each set related from 52% to 95% by pedigree, have been profiled for 85 mapped RFLP probes. Associations among lines on the basis of RFLP and pedigree data were revealed by principal component and cluster analysis. F1 yield and heterosis data, which were calculated on the basis of inbreeding depression incurred between the F1 and F2 generations, were collected during 1987 and 1988 at 5 locations with 3 replicates per location, 60 plants per replicate. All generations of seed were made simultaneously in the same year and location. Inter-line distances calculated from RFLP data showed correlations with distances calculated from pedigree records of (Malecot's coefficient of kinship) r = 0.97, with F1 yield r = 0.76, and with heterosis r = 0.56. Pedigree data resulted in correlations with F1 yield of r = 0.62 and with heterosis r = 0.66. In comparison, HPLC zein data gave correlations with F1 yield of r = 0.34 and heterosis of r = 0.54. These data show that associations on the basis of RFLP data among these relatively closely related lines agree well with those that would be expected on the basis of known pedigree.

For the first time we have found a laboratory derived data base (RFLP's) that provides a more accurate prediction of F1 yield than do pedigree data. We expect that this is due to the large number of marker "loci" and the abundance of variants that, therefore, allow chromosomal regions to be tracked from parents to progeny with a degree of detail that was hitherto unafforded by isozymic or zein protein data. We suspect that the relatively low correlation between distances measured by RFLP data and heterosis compared to that shown between RFLP and F1 yield data may be due to the reduced ability to accurately measure heterosis between the relatively closely related inbred lines used in this study. In these lines, the average performance of the F2 generation would likely be similar to that of the inbred line per se and the relatively poor performance of the inbred compared to the F1 generation can result in biased estimates of heterosis.

We are continuing on from these preliminary analyses by looking at associations among a larger set of less closely related inbred lines estimating correlation between field, pedigree, and laboratory data. This set of data also includes the immense power of analysis afforded by the technique of two-dimensional gel electrophoresis which reveals in qualitative and quantitative fashion on the order of 1,000 individual protein products for each inbred line (see Higginbotham, Smith, and Smith in this Newsletter).

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