A method has been developed for estimating the value of donor lines or populations for improving an elite single cross. The method provides estimation of lp(l)muBAR: the relative number of dominant alleles in a potential donor line or population at loci for which an elite single cross to be improved is homozygous recessive. The method also allows estimation of jp(j)muBAR, jq(j)muBAR, kp(k)muBAR, and kq(k)muBAR: the relative numbers of alleles in a potential donor at loci for which the elite single cross is heterozygous. This experiment was conducted to determine whether these estimators correctly rank populations with known relative values of lp(l)muBAR, jp(j)muBAR, and kp(k)muBAR. Maize (Zea mays L.) hybrid FRB73 x FRMo17 was the elite single cross to be improved; 15 potential donors were selected. Populations containing 75, 50, and 25% germplasm from individual donors were produced by crossing each donor to FRB73 X FRMo17 and backcrossing to each parent. Estimates of lp(l)muBAR, jp(j)muBAR, jq(j)muBAR, kp(k)muBAR, and kq(k)muBAR were obtained for grain yield, earliness of flowering, plant height, and ear height. For each donor, estimates were calculated for populations with 100, 75, 50, 25, and 0% donor germplasm (the 100% population was the donor and the 0% population was the elite single cross itself). These five populations correspond to proportions of 1.0, 0.75, 0.50, 0.25, and 0.0 times lp(l)muBAR, respectively. For jp(j)muBAR and kp(k)muBAR, p(j) and p(k) are 0.5 in FRB73 x FRMo17 and may be larger or smaller in the donor. Linear regression of estimates on proportion of donor germplasm was performed using the array of populations from each donor. In general, when estimates of lp(l)muBAR, jp(j)muBAR, or kp(k)muBAR for the donors (100% populations) were significantly different from those of the F1, the proportion of variation explained by linear regression was highly significant. In addition, when estimates of lp(l)muBAR were averaged across populations of each proportion, linear regression on proportion of donor germplasm accounted for 87 to 99% of the variation among mean estimates for all traits. Because estimators precisely rank lines or populations relative to frequencies of useful new alleles to improve an elite single cross, they should be useful in selecting parents to improve single crosses.
