Variability and inbreeding in semiexotic maize populations.

Three semiexotic populations (CRE-01, CRE-02, CRE-03) obtained by incorporation of exotic germplasm (lines from CIMMYT, Colombia; selected for resistance to corn stunt complex) were evaluated in two cycles of recurrent selection with half-sib families. In cycle-I, samples comprising 50, 70, and 50 half-sib families were evaluated at Jataí (GO) and traits analyzed were ear yield, plant height, and ear height. For yield (t/ha), populations means were 5.86, 6.19, and 5.31, representing approximately 73% of hybrid check. Sets of parameters estimates representing the three populations were: [237, 485, and 608] for the additive genetic variance (σ(2)A: g/plant); [0.393, 0.584, 0.658] for the coefficient of heritability (h(2)m: progeny mean basis), and [0.464, 0.684, and 0.801] for the index of variation (θ). In cycle-II, materials analyzed included 60 non-inbred (half-sib) and 60 inbred (S1) families from each population, evaluated at Anhembi (SP) with two replications; traits analyzed included ear yield plus ear weight and grains weight of four ears, two plant traits (plant height and ear height), two ear traits (length and diameter), two tassel traits (branch number and length), and resistance to corn stunt complex. Means of half-sib families for ear yield (t/ha) were [10.614, 10.419, 10.842], representing 83 to 86% of the hybrid check. The same pattern of variation was observed for ear weight and grain weight of four ears. Means of S1 families were [6.465, 5.527, 5.925] and the inbreeding depression in percent of the non-inbred families were [39.1, 46.9, 45.3]. Estimates for other traits are also shown.