ALTERING SOURCE-SINK RELATIONSHIPS IN PROLIFIC MAIZE HYBRIDS - CONSEQUENCES FOR NITROGEN UPTAKE AND REMOBILIZATION

Competition between grain and roots for photoassimilates may reduce po st-anthesis N uptake (N-a), thereby limiting grain production of proli fic maize (Zea mays L.). Field experiments were conducted to determine if this competition was minimized during the selection for new high-y ielding prolific lines, providing a plausible physiological explanatio n for the improved grain yields. The dry matter (DM) and N accumulatio n and partitioning of two high-yielding and three low-yielding prolifi cs were compared under full pollination, limited pollination of the ap ical ear, or no pollination. The following year, one high-yielding and one low-yielding hybrid were grown at 34 000 and 45 000 plants ha(-1) . Fully pollinated, high-yielding hybrids averaged 74% more grain weig ht (G(w)) than low-yielding hybrids. A high-yielding hybrid produced 7 1% more G(w) under full pollination than with apical ears only pollina ted, while limiting pollination had little effect on low-yielding hybr ids. Greater contributions of subapical ears in new prolifics were att ributed to greater kernel weight and number, which were positively cor related with post-anthesis DM accumulation (T-wa). The DM partitioning to vegetative tissue [T-wa - G(w)] is an indicator of photosynthate a vailability for plant functions during grain-filling. Greater [T-wa, - G(w)] occurred at the low plant density and with limited pollination, and this was positively related to N-a while inversely related to N-r . The high-yielding hybrids maintained T-wa and N-a during multiple ea r development. These results suggest N-a is regulated by the ear sink size relative to photosynthate supply.