Reproductive Growth in Stacked and Non-Stacked Maize Hybrids.

Stacked hybrids of maize represent an increasing part of the offer in the seed market and a comparable grain yield of both stacked hybrids and their non-stacked counterparts is strongly promoted by seed companies. However, the performance of both groups of hybrids when grown under absence of pests and weeds is less known. The objective of this study was to compare stacked and non-stacked near isoline maize hybrids growing under moderate and high plant population in terms of grain yield and its eco- physiological components during reproductive stages. The experiment was carried out at INTA Paraná Research Station during 2007/8 growing season and included a standard maize hybrid (DK747), and their genetically modified versions: DK747 MG and DK747 MGRR. Experiment was conducted without nutrient deficiency and both pests and weeds were controlled by using chemical and mechanical ways. Grain yield and several physiological components during reproductive stages (i.e., R1-PM) as light interception (RI), radiation use efficiency (RUE), crop growth rate (CGR_R1+15) and dry matter partitioning were evaluated. Grain yield ranged between 1241 g m^-2 and 1397 g m^-2 for non-stacked and stacked hybrids, respectively (p=0.0287). Stacked hybrids showed greater kernel number (9.7%, p<0.10) than its non-stacked counterpart, it also trended to increase kernel weight (3%) and harvest index (7%). No significant interactions were observed between hybrids x plant populations on all crop variables examined. Both groups of hybrids showed comparable values of RI, RUE and CGR_R1+15 during reproductive stages. However, as plant population increased the proportion of dry matter allocated to ear around silking was greater in stacked than non-stacked hybrids (0.45 vs.0.34). Our results indicate that pleiotropic effects in transgenic hybrids could improve performance of stacked hybrids.