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

Competition between grain and roots for photoassimilates may reduce post-anthesis N uptake (N-a), thereby limiting grain production of prolific maize (Zea mays L.). Field experiments were conducted to determine if this competition was minimized during the selection for new high-yielding prolific lines, providing a plausible physiological explanation for the improved grain yields. The dry matter (DM) and N accumulation and partitioning of two high-yielding and three low-yielding prolifics were compared under full pollination, limited pollination of the apical 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 weight (G(w)) than low-yielding hybrids. A high-yielding hybrid produced 71% more G(w) under full pollination than with apical ears only pollinated, while limiting pollination had little effect on low-yielding hybrids. Greater contributions of subapical ears in new prolifics were attributed to greater kernel weight and number, which were positively correlated with post-anthesis DM accumulation (T-wa). The DM partitioning to vegetative tissue [T-wa - G(w)] is an indicator of photosynthate availability 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 ear development. These results suggest N-a is regulated by the ear sink size relative to photosynthate supply.