Influence of Pollination Pattern on Intrapanicle Caryopsis Weight in Sorghum

Recent studies have shown that changes in grain‐fill rates within the sorghum [ Sorghum bicolor (L.) Moench] panicle cause caryopsis weights to decrease from the apex to the base. Pollination pattern in the sorghum panicle is also basipetal. The objectives of this study were to determine if pollination pattern influences intrapanicle caryopsis weights and to determine which components of grain fill are affected by pollination pattern. Field studies were done in 1990 at Manhattan, KS, on a Reading silt loam [fine‐silty, mixed, mesic Typic Argiudoll (0–1% slope)] and Hays, KS, on a Barney silt loam [fine, montmorillonitic, mesic Typic Argiustoll (0–1% slope)]. At Manhattan, eight pollination‐pattern treatments were applied to DeKalb DK 46 and its male‐sterile parent, 97A. At Hays, a male‐sterile hybrid, KS56A × KS47B, received four of the eight treatments. Panicles were divided into four equal sections; apex, upper middle, lower middle, and base. Different pollination patterns were applied to the sterilized panicles by exposing the appropriate sections to pollen. Differences in caryopsis weights and weight components were determined using analysis of variance and linear regression analyses. In all cases, intrapanicle caryopsis weights followed the pollination pattern applied. The panicle sections pollinated first had caryopses that were from 1.0 to 2.5 mg heavier than those found in the sections pollinated later. Pollination pattern influenced caryopsis weight by influencing grain‐fill rates within the panicle; the length of the grain‐fill period did not change. Apparently, caryopses that were pollinated first were better competitors for assimilates than those pollinated later.