Random mating before selfing in maize BC₁ populations

In maize (Zea mays L.) inbred development programs, F₂ and BC₁ populations between two inbreds are usually not random-mated before selfing. Previous results suggest random mating is not useful in F ₂ populations. A one-locus model, however, suggests random mating increases the genetic variance by 50% in a BC₁ population without affecting the population means. The objective of this study was to determine the effect of random mating on the testcross means and variances of BC ₁ populations. Random-mated and nonrandom-mated backcross populations were developed for two genetic backgrounds, Iowa Stiff Stalk Synthetic (BSSS) and non-BSSS. Testcrosses of these four populations were evaluated at five locations in Minnesota and Wisconsin in 2002. For grain yield, gram moisture, plant height, ear height, root lodging, and stalk lodging, the differences between test-cross means of random-mated and nonrandom-mated populations were not significant (P = 0.05), as expected. Testcross variances tended to increase with random mating for most traits in the two genetic backgrounds, but none of these differences was significant. Testcross means of the best 10% families did not differ significantly between random-mated and nonrandom-mated populations. Overall, the results indicated that random mating before selfing in BC₁ populations is not useful in applied breeding programs.