Kernel Weight Increase in Response to Decreased Kernel Number in Sorghum

AbstractProcesses involved in the increase of individual kernel weight (KWT) in sorghum [Sorghum bicolor (L.) Moench] in response to reduced kernel number per panicle (KNO) have not been investigated. A better understanding of these would aid modelers in predicting grain yield, and crop physiologists in understanding yield component compensation. This study examined whether rate of kernel filling, effective filling period (EFP), or both were responsible for the increase in KWT. A widely used single‐seeded hybrid, ‘ATx399 × RTx430’, and an expermental twin‐seeded hybrid, ‘ATx623 × 77CS256TS’, were grown on a Houston black clay (fine, montmorillonitic, thermic Udic Pellustert) at Temple, TX, in 1985 and 1986. Seventy‐nine percent shading during the 16 d prior to 50% anthesis caused KNO to be reduced by 72%. Kernels from the apical, middle, and basal portions of the panicles were sequentially harvested to determine the rate of filling and the EFP. Kernel weight of these shaded plants was 31% greater than for the control. Effective filling period for shaded plants was not increased significantly compared to the control. Rate of filling was, therefore, the primary means by which the increased KWT was attained. Neither the number of endosperm cells per kernel 10 to 16 d post‐anthesis nor the number of starch granules per kernel 14 to 16 d post‐anthesis were increased significantly by shading. Number of starch granules was three times greater at maturity than at 14 to 16 d post‐anthesis, and was significantly greater for the shaded treatment. While final kernel volume was greater for the shaded plants, a volume limitation did not appear to be the cause for the difference in dry weights. Kernel dry weight was already different between treatments by the time maximum volume was achieved. Further investigation is needed to determine the reasons for the increase in both rate of filling and KWT in response to decreased KNO.