ASSIMILATE ENHANCEMENT ON PLANT-GROWTH RATE AND FINAL WEIGHT OF MAIZE KERNELS

There are several studies showing that maize (Zea mays L.) final yield is limited by the availability of assimilates during the grain filling period. With the objective of studying assimilate enhancement on the duration of grain filling period, plant growth rate and maize final kernel weight, a field experiment was conducted in Saint Paul, MN, USA, with two genotypes: hybrid M14 x W64A and the cultivar Pioneer 3780. The treatments consisted of partial kernel removal (tip half of the ear) and thinning by 50% plant population reduction, imposed at 6 and 24 days after silking. The results showed that 14 x W64A responded to early thinning, as indicated by an extended grain filling period. Thinning and partial kernel removal on both dates increased internode dry weight and final kernel weight. Pioneer 3780 was not affected by treatments. Although the treatments were effective in some cases, they did not always lead to a significative increasing in the kernels dry weight. This may suggest that the assimilate supply is not the principal limitation for the grain yield. This limitation may be controlled by intrinsic factors of the seed itself. The efficiency of the invertase activity may also be considered.