Grain yield and kernel setting of multiple-shoot and/or multiple-ear maize hybrids

Rainfed maize (Zea mays L.) crops in low-rainfall regions are cultivated at very low plant population densities that favor the production of fertile tillers or multiple ears in the main shoot. Little information exists regarding the functional processes governing grain yield and kernel setting on ears of different order of shoots of maize crops. To study these functional processes, field experiments were conducted cultivating two commercial maize hybrids (AX7784 and DM2738) under supplementary irrigation using different plant densities, N rates at sowing, shading around female flowering (silking) and tiller removal treatments. Hybrids differed in the number of tillers per plant at R1 (AX7784 > DM2738). Early tiller removal increased main shoot growth rate around silking, suggesting competition for light among shoots. Kernel number per plant was positively and curvilinearly related with plant growth rate around silking, i.e. critical period (PGRCP), in tillered and non-tillered plants of both hybrids. Tillered plants set higher kernel numbers than non-tillered plants at PGRCP > 9 g pl-1 d-1 (AX7784) or 11 g pl-1 d-1 (DM2738), while the opposite trend occurred at PGRCP values < 9 g pl-1 d-1 (both hybrids). In both hybrids, the combination of a higher biomass partitioning to but a lower reproductive efficiency of ears of tillers than of main shoots resulted in a lower kernel number for tillers than for main shoots. Genotypic differences were evident in kernel setting between main shoots (DM2738 > AX7784) and tillers (AX7784 > DM2738). The different pattern of kernel setting between hybrids was explained by differences in the biomass partitioning to tiller ears and the reproductive efficiency of ears of tillers (AX7784 > DM2738), and both the biomass partitioning to and the reproductive efficiency of second and third order ears of main shoots (DM2738 > AX7784). Kernel number per plant was higher for DM2738 due to a higher kernel setting on multiple ears of main shoot plus tillers (more prolific and with lower tiller fertility) than for AX7784 (less prolific and with higher tiller fertility). However, grain yield did not differ between hybrids, because of the higher kernel weight of AX7784. Therefore, this work opens avenues for exploiting higher grain yields in maize crops with low plant population densities through the combination of prolificacy and tillering. Further studies should analyze the impact of reproductive plasticity on kernel weight determination in low-density maize crops.