Further Analysis of the Mating System in Two Mass Selected Populations of Maize1

Abstract

In order to determine whether main stalks (MS) and tillers (T) outcross at different rates, estimates of the amount of outcrossing (t) vs. self‐fertilization (s = 1 − t) were made at nine enzyme loci in MS and T fractions of two maize (Zea mays L.) populations that had been mass selected for prolificacy [NHG(M)P‐17] and grain yield [NHG(M)C‐22]. The weighted mean single‐locus estimates of t were 0.96 for P‐17MS, 0.92 for P‐17T, 0.82 for C‐22MS, and 0.95 for C‐22T. The multilocus outcrossing values were 1.00, 0.93, 0.83, and 0.93. The results show that outcrossing was the predominant form of mating in all population fractions, but a substantial amount of selfing (9%) also occurred. The P‐17 population selected for prolificacy selfed at a lower rate (4%) than the C‐22 population selected for increased grain yield (12%). The rate of selfing was similar in T fractions of both populations (7%), but MS selfed at a higher rate (17%) in C‐22 than in P‐17 (0%). This suggests a possible advantage to using MS samples when selecting for increased prolificacy in ‘Hays Golden’ germplasm. The results also suggest that for the C‐22 population greater progress from mass selection for high grain yield would occur if progeny from T ears (t = 0.93) were used to form the successive generation rather than progeny from MS ears (t = 0.83).