Genetic variances and correlations in an early tropical white maize population after three cycles of recurrent selection for Striga resistance

The magnitude and type of genetic variability are of prime importance to breeders in determining whether or not to improve a breeding population and the method to use. The early maturing population, TZE-W Pop DT STR, has gone through three cycles of S1 recurrent selection for improvement for grain yield and Striga resistance. Three hundred full-sib families within half-sib groups from cycle 3 of TZE-W Pop DT STR were evaluated under artificial Striga infestation in Ferkéssedougou, Côte d’Ivoire, 2002, and in Mokwa, Nigeria, 2003. Estimates of additive genetic variances were positive and moderate-to-large for all traits except lodging percentage. The additive genetic variance was much larger than the dominance variance for all traits except Striga emergence count. The dominance variance for Striga emergence was about twice as large as additive genetic variance at 8 WAP and about four times as large at 10 WAP. Narrow sense heritability (h2) estimate was 25% for grain yield and 0-90% for 13 other traits. The wide ranges, moderate-to-large additive genetic variance and expected gain/cycle of selection, and moderately low-to-high narrow sense heritability estimates observed in TZEE-W Pop DT STR C3 indicate that sufficient residual genetic variability still exists in the population to allow further improvement for grain yield, Striga resistance, and most other traits in the population. A wide range of genetic variation was observed among the full-sib families from TZE-W Pop DT STR C3 in Striga emergence count and Striga damage rating and several progenies were identified that combined reduced Striga emergence and Striga damage implying that it should be possible to extract from the population experimental varieties that combine both low Striga emergence and Striga damage. Grain yield had a large positive additive genetic correlation with EPP, a large negative genetic correlation with Striga damage ratings, and moderately large negative genetic correlations with flowering traits and Striga emergence count at 10 WAP