RELATIONSHIP BETWEEN OCCURRENCE OF POORLY RIPENED GRAINS AT THE EAR TIP AND PRODUCTION OR PARTITIONING OF DRY-MATTER IN SWEET CORN

The causes of the development of poorly ripened grains (PRG) at the tip of 'Honey Bantam 36' sweet corn ear based on dry matter production, leaf cutting, shading, and thinning after silk emergence on the development of unfilled grains (UG), were investigated. 1. Leaf cutting and shading resulted in the increase of PRG, whereas thinning and sparse planting caused it to decrease compared to the control. The occurrence of UG, consisting of PRG and unfertilized grains had a high significant, positive correlation with the occurrence of PRG. 2. Alteration of the total dry weight by thinning and shading after silk emergence affected the supply of assimilates to ear. Variations in the occurrence of PRG caused by the alteration of the supply of assimilates affected the unfilled tip length and the occurrence of UG. 3. When plants were grown under the same conditions during the first period (vegetative phase) and later thinned and shaded, the occurrence of UG correlated well with the dry matter accumulation during the grain filling period. 4. When plants were grown under different conditions during the first period and then placed under the same conditions (equal plant density), the occurrence of UG correlated with dry matter production during the first period. When dry matter production during the first period increased, the partitioning of the dry matter to the ear during the second period increased. 5. Partitioning of the dry matter within the ear differed significantly between kernals at the tip and at the base. The dry matter within shaded ears was partitioned away from the tip and toward the basal position of the ears as compared to the control. 6. Dry matter accumulation during grain filling did not differ among treatments whereas the occurrence of UG did. This is attributed to a decreased translocation from stem to ear, especially to the ear tip. We conclude that the development of poorly ripened grains is influenced by (i) dry matter accumulation during grain filling, (ii) the amount of dry matter accumulated prior the grain filling, and (iii) the translocation of current photosynthates to the ear, especially to its tip.