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 ti p of 'Honey Bantam 36' sweet corn ear based on dry matter production, leaf cutting, shading, and thinning after silk emergence on the develo pment of unfilled grains (UG), were investigated. 1. Leaf cutting and shading resulted in the increase of PRG, whereas thinning and sparse p lanting caused it to decrease compared to the control. The occurrence of UG, consisting of PRG and unfertilized grains had a high significan t, positive correlation with the occurrence of PRG. 2. Alteration of t he total dry weight by thinning and shading after silk emergence affec ted 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 gro wn under the same conditions during the first period (vegetative phase ) and later thinned and shaded, the occurrence of UG correlated well w ith the dry matter accumulation during the grain filling period. 4. Wh en plants were grown under different conditions during the first perio d and then placed under the same conditions (equal plant density), the occurrence of UG correlated with dry matter production during the fir st period. When dry matter production during the first period increase d, the partitioning of the dry matter to the ear during the second per iod increased. 5. Partitioning of the dry matter within the ear differ ed significantly between kernals at the tip and at the base. The dry m atter within shaded ears was partitioned away from the tip and toward the basal position of the ears as compared to the control. 6. Dry matt er accumulation during grain filling did not differ among treatments w hereas the occurrence of UG did. This is attributed to a decreased tra nslocation from stem to ear, especially to the ear tip. We conclude th at the development of poorly ripened grains is influenced by (i) dry m atter accumulation during grain filling, (ii) the amount of dry matter accumulated prior the grain filling, and (iii) the translocation of c urrent photosynthates to the ear, especially to its tip.