VARIETAL DIFFERENCES IN GRAIN FILLING AT THE DISTAL END OF SWEET CORNEAR

The bases of varietal differences in the frequency of unfilled grains at the distal end of sweet corn cultivars in relation to : (i) the dry matter production, (ii) partitioning of dry matter within the ear, an d (iii) changes in the florets with emerged silk were investigated. 1. Cultivars with delayed silk emergence had the largest total plant dry weight at silking time, the fastest dry matter accumulation rate durin g grain filling, heaviest ear weight at the harvesting, and the maxima um number of filled grains. A low negative correlation was obtained be tween the percentage of unfilled grains and dry matter accumulation du ring grain filling period. 2.A positive correlation exists between per centage of the decrease of a single grain weight (SGW) at the distal p ositions and percentage of the occurrence of unfilled grains on the ea r. Ears on cultivars which have significantly lighter SGW at the ear d istal end compared to the basal grains had large proportions of unfill ed grains. 3.A negative correlation exists the percentage of the flore ts with silk emerging 5 days after the first silk appearance and perce ntage of the decrease of a SGW at the distal end of the corn ear. The difference in SGW within an ear was small in the cultivars in which si lk emerged relatively early, proceeding from the basal to the distal f lorets. Therefore, the varietal difference in the frequency of unfille d grains are caused, not only by the dry matter accumulation during gr ain filling, but also by the partitioning of assimilates to the distal grains. Cultivars in which silk emerged relatively early had : (i) un iform partitioning of dry matter within ear, (ii) greater translocatio n of assimilate to the distal grains, and (iii) fewer unfilled distal grains.