Inbreeding depression effects in advanced generations of four genetic types of maize hybrids

Abstract

The experiments were conducted in two locations: Sete Lagoas, MG and Guaíra, SP, Brazil. A split-plot field design in three replications was used with hybrids as main plots and "Sib" and F₂ plants as sub-plots. Inbreeding effects were studied in advanced generations of single, three-way, double and variety cross hybrids. Seeds for this study were obtained from Agroceres, Germinal and CNPMS. The results showed that within each group, single, three-way and double cross hybrids had all similar inbreeding effects for grain yield. Generally, in the self-fertilizing generations (F₂) and (Sib) for the four hybrids groups, there were an increase in plant cycle and a significant decrease in plant and ear heights. Double and three-way hybrids had higher yielding than the single (SH) and variety cross hybrids groups. For grain yield, the mean inbreeding depression effects in the hybrids, were greater for selfing generation (F₂) with 46% and 47% for Sete Lagoas and Guaíra, respectively, than the Sib generation, with 25% and 26% for Sete Lagoas and Guaíra, respectively. The mean inbreeding depression (F₁ - Sib) values were 20% for double crosses, 30,5% for three-way crosse, 27% for single crosses and none for variety cross hybrids. The mean depression values due to self- -fertilization (F₁ - F₂) were 50%, 47,5% 41% and 47% for double, three-way, single and variety cross hybrids, respectively.