FACTORS CONTROLLING CARYOPSIS DEVELOPMENT AT THE EAR TIP OF SWEET CORN

To determine the causes of the development of the unfilled grains cons isting of unfertilized and poorly ripened grains at the tip of an ear of sweet corn (cv. Honey Bantam 36), the relationships between (i) pol len shedding time and pollen viability, (ii) silk (style) elongation a nd pollination/fertilization time of florets, and (iii) the fertility of florets and filling ability of caryopses were investigated. 1. Poll en shedding from tassel florets lasted from 2 days before to 6 days af ter the first silk appearance (FSA). The germination ratio of the shed ded pollen decreased significantly 6 days after FSA. 2. Silk emergence from florets proceeded acropetally; silk from the 30 th to 40 th tip florets from the base of the ear emerged 4 to 6 days after FSA. These silks were pollinated and the egg in the overy fertilized between 6 to 8 days after FSA. 3. Bagging an ear to prevent open-pollination resul ted in mostly unfertilized grains; whereas, comparable hand-pollinatio n developed into normal, filled grains. Consequently, florets at the e ar tip were receptive and capable of developing into normal grains as late as 10 days after FSA. 4. Hand-pollination florets, 6 days after F SA under natural conditions (without bagging), resulted in partially f illed grains. We attribute the presence of unfertilized grains at the corn ear tip to lack of viable pollen for pollination and the developm ent of the poorly ripened grains to an insufficient supply of current photosynthates.