A Study of the Breeding Potential of a Population of Alfalfa (Medicago sativa L.)

Summary Improved cultivars are the goal of all forage-breeding programs. In alfalfa (Medicago sativa L.), great improvements have been made in pest resistance and stability of performance, but little has been accomplished in improving yield potential. This lack of improvement in yield potential may be due to selection for yield under noncompetitive conditions. The objective of this study was to evaluate the breeding potential of an alfalfa population when selection was based on performance under competition. A heterozygous alfalfa population, consisting of F₁ families from crosses between synthetics BW1 and BW9, was used in the study. The F₁ families and polycross progenies of random plants from within each F₁ family were evaluated in a simulated sward under growth-room conditions. Dry-matter yield was measured over three harvests. The additive and digenic variances and the narrow-sense heritability for dry-matter yield of the F₁ population were estimated from the analyses of variance. A number of 1096-clone synthetics were developed from the F₁ population to determine the response to selection. The estimates of additive variance were significant for dry-matter yield at the second harvest and for total yield. None of the digenic variance estimates was significant. This lack of significance indicates that the genetic variance in this population was mainly additive, with a narrow-sense heritability for total dry-matter yield of 15%. The genetic coefficient of variation was greatest within the original population of F₁ families. Significant position correlations between the F₁ population and polycross progeny yields and the presence of significant additive variance indicated a potential for improving the F₁ population through phenotypic mass selection. Comparisons between the experimental synthetics and an unselected bulk of all F₁ families indicated that no response to selection was apparent. Although the mean yield of 4 synthetics at the Syn-3 generation was 7% above that of the bulk, this difference was not significant. Further cycles of selection or a change in the experimental design may be required to detect differences. Judging by these results, selection gains for yield could be made in this population of alfalfa. Further cycles of mass selection, conducted under sward conditions, are warranted.