Source: sink ratio and leaf senescence in maize: I. Dry matter accumulation and partitioning during grain filling

Whether the stay-green characteristic of recent maize hybrids is related to a larger source : sink ratio and/or a more efficient use of N during repro ductive development was studied in a 3-year field experiment. The experimen t was conducted with two short-season maize hybrids, Pride 5 told) and Pion eer 3902 (recent), grown at two soil-N levels and with source:sink treatmen ts during grain filling ranging from partial defoliation to no grain. Resul ts confirmed that greater dry matter accumulation of Pioneer 3902, relative to Pride 5, was associated with greater leaf longevity. Change in stover w eight from silking to maturity an indicator of the difference in supply and demand of assimilates during grain filling, varied from -30% with defoliat ion to +25% for the no sink treatment. The change was always greater in the new hybrid, indicating that the old hybrid was more source limited. Number of green leaves, an indicator of leaf longevity, was greatest when supply and demand of assimilates during grain filling were approximately equal. Le af longevity was enhanced by an increase in soil N and the effect was large r in the high source:sink treatments, but differences in leaf longevity bet ween the two hybrids were not influenced by soil-N level. In conclusion, in creased leaf longevity of a new relative to an old hybrid was associated wi th a larger source : sink ratio during grain filling. (C) 1999 Elsevier Sci ence B.V. All rights reserved.