Maize Ear Development in Response to Nitrogen Availability: Differences Between Hybrids with Contrasting Tolerance to Increased Stand Density.

In maize (Zea mays L.), previous studies indicate that the total number of completely developed flowers per ear is not affected by contrasting assimilate availability per plant such as those promoted by contrasting plant population, sowing dates, nutrient regimes and water availabilities. The objective of this work was to evaluate ear floret development under contrasting N availability levels and its effects on final kernel number and grain yield in two hybrids with contrasting tolerance to crowding stress. Field experiments were conducted during two growing seasons using a factorial combination of (i) two N levels (N0: no N added; N200: 200 kg N ha^-1 applied at V₆), (ii) two maize hybrids of contrasting tolerance to increased stand density (tolerant: AX820CL-MG; intolerant: AX877CL-MG), and (iii) two stand densities (9 and 12 pl m^-2). Floret development of the uppermost ear-shoot was surveyed between V₆ and silking, and kernel number per ear was determined at physiological maturity. There were significant differences (p<0.05) in number of completely developed flowers per row at V₁₃ promoted by low nitrogen. For both hybrids, the apical ear exhibited a delayed progress rate to floral stages and lower kernel number.  These results contrast with previous evidence on this topic, which reported no effects of resource availability on ear morphogenesis.