Nonrandom Mating in Experimental Populations of Maize1

Abstract

Eight enzyme loci were used to estimate the amount of outcrossing vs. self‐fertilization in two maize (Zea mays L.) populations, NHG(M)C‐21 and NHG(M)P‐16, that were developed recurrent mass selection for high yield and prolificacy, respectively. Single‐locus and multilocus estimates of outcrossing (t) and selfing (s = 1 − t) were made in selected (C‐21S and P‐16S) and unselected (C‐21 and P‐16) samples from each population. Single‐locus outcrossing values fluctuated widely from locus to locus in each of the four samples. The weighted mean single‐locus estimates of outcrossing were 0.91 ± 0.03, 0.94 ± 0.03, 0.88 ± 0.03, and 0.82 ± 0.03 (t = 0.89 ± 0.02) for C‐21, C‐21S, P‐16, and P‐16S, respectively; the multilocus (8‐locus estimate) outcrossing estimates were 0.81 ± 0.02, 0.88 ± 0.02, 1.00 ± 0.02, and 0.91 ± 0.02 (t = 0.90 ± 0.01). These results show that approximately 10% self‐pollination occurred in these populations, and that as a result the populations contain homozygotes in excess of mating expectations immediately after the mating cycle. However, in general, adult genotypic frequencies fit binomial square expectations which suggests that selection favoring heterozygotes occurred between seedling and adult stages of the life cycle.