Caryopsis Weight Patterns within the Sorghum Panicle

Understanding the intrapanicle pattern of caryopsis weights commonly found in sorghum [ Sorghum bicolor (L.) Moench] fields and the factors that result in changes in this pattern would help in determining limitations on caryopsis weight. Our objectives were to determine the pattern of caryopsis weights found in the sorghum panicle, the effect of assimilate supply on the weight pattern, and whether this pattern resulted from the rate of grain fill or length of the effective fill period (EPP). Two dryland field studies were conducted at Manhattan, KS, in 1989 and 1990 on a Reading silt loam (fine‐silty, mixed, mesic Typic Argiudoll; 0–1% slope). In 1989, panicles of DeKalb ‘DK 46’ and Pioneer ‘8500’ tagged at anthesis were harvested at regular intervals. In 1990, seven population‐light treatments were applied to Pioneer 8500 either at anthesis or 7 d after anthesis. Panicles from both experiments were separated into four sections. Caryopses from these sections were used to determine differences in caryopsis weights, rate of grain fill, and length of the EPP. In 1989, caryopsis weights within the sorghum panicle increased from 20.2 mg caryopsis −1 at the base to 22.8 mg caryopsis −1 at the apex. In 1990, this same intrapanicle pattern was observed in all treatments that had medium or high plant populations during the EPP. This pattern was caused by increases in the rate of grain fill from the base to apex of the panicle. In the low population treatments in 1990, caryopses in the middle of the panicle were as heavy or heavier than those in the apex. This was the result of intrapanicle grain‐fill rates that were more uniform and an increase in the length of the EPP from the apex to the base of the panicle.