Secondary traits related to kernel setting in transgenic maize hybrids at low and high plant densities and their potential use in breeding programs

Maize (Zea mays. L) traditional breeding presents limitations when selection is performed by adaptation to suboptimal conditions. One strategy to achieve greater efficiency in these environments is to include measurements of secondary traits related to the main grain yield component, i.e. kernel number per plant (KNP), which is associated to other three secondary traits: plant growth rate during the critical period (PGRcp) for kernel setting, biomass partitioning index to the ear during this period (PIcp) and the efficiency of the ear to set kernels or reproductive efficiency (RE). Phenotypic variations in these KNP related traits were evaluated considering: i) plant densities, and ii) simple and staked transgenic maize hybrids. The objective of this study was to identify the contribution of these secondary traits to KNP in six modern single-cross transgenic hybrids: the simple and staked transgenic versions of DK747 and DK190 (Bt: 747MG and 190MG; RR: 747RR and 190RR; and Bt-RR: 747MGRR and 190MGRR) cultivated at low and high plant densities. For this purpose, KNP and secondary traits were recorded at the individual plant level and data set was analyzed using multivariate analysis techniques. At low plant density, PGRcp was the critical trait for kernel setting in all hybrids but PIcp or RE also contributed to KNP of the DK747 group and the D190 group, respectively. At high plant density, a differential contribution of secondary traits to KNP was recorded among hybrids. For DK747MG and DK190MG, RE mainly determined KNP, but for the DK747RR and DK747MGRR higher PIcp had positive impact on KNP. These results highlight the importance of including secondary traits associated to KNP in breeding programs.