Monitoring protein quality of o2 maize (Zea mays L.) in inbred lines and their F₁ and F₂ progeny

Because of its high contents of essential amino acids lysine and tryptophan, opaque-2 (o2) maize (Zea mays L.) is an option for improving human nutrition in social sectors whose diet is based on maize. For this reason, its genetic improvement is relevant. This study analyzed the o2 maize hybrids from the parent lines up to the generation of grain for consumption (F₂). The objectives were to determine the contents of tryptophan, lysine and total protein and the quality protein index of the six o2 maize lines, of the 15 single crosses formed with these lines and the F₂ generation of these crosses, as well as to observe whether these variables decreased between F₁ and F₂. The o2 maize lines (M1 to M6) and the 15 single direct crosses formed with these lines were sown in 2011, whereas generation F₂ of the crosses and H70 (regional control) were sown the following year. The experimental design was completely randomized with two replications. Contents of lysine, tryptophan and total protein and the quality protein index were determined in harvested grain of each genotype, and differences in these values between F₁ and F₂ were estimated. Lines M2 and M3 and the crosses M2 x M4, M2 x M6 and M3 x M6 had higher contents of lysine, tryptophan and total protein and a higher quality protein index. Protein quality was not stable in F₂, with the exception of M3 x M6, which maintained the ICP in this generation and was the most consistent and stable cross. Inbreeding depression did not affect the crosses with intermediate protein quality (M2 x M5 and M5 x M6) nor did it affect lysine content, which was the experimental variable with the best response in all of the breeding stages.