Methods to evaluate populations for alleles to improve an elite hybrid.

Elite hybrids can be improved by the introgression of favorable alleles not already present in the hybrid. Our first objective was to evaluate several estimators derived from quantitative genetic theory that attempt to quantify the relative number of useful alleles in potential donor populations. Secondly, we wanted to evaluate two proposed ways of determining relatedness of donor populations to the parents of the elite hybrid. Two experiments, each consisting of 21 maize populations of known pedigree, were grown at three and four environments in Minnesota in 1991. Yield and plant height means were used to provide estimates of each of the following statistics: (1) LPLU, a minimally biased statistic, (2) UBND, the minimum estimate of an upper bound, (3) NI, the net improvement, (4) PTC, the predicted three-way cross, and (5) TCSC, the testcross of the populations. These statistics are biased estimators of the relative number of unique favorable alleles contained within a population compared to a reference elite hybrid. Based on rank correlations, all statistics except NI ranked populations similarly. The percent novel germplasm relative to the single cross to be improved was positively correlated with the estimates of favorable alleles except when NI was used as the estimator. The relationship estimators agreed with the genetic constitution of the donor populations. Strong positive correlations existed between diversity, based on the relationship rankings, and all the estimator rankings, except NI. Potential donor populations were effectively identified by LPLU, UBND, PTC, and TCSC. NI was not a good estimator of unique favorable alleles.