Partitioning of 14C‐Photosynthate and Biomass in Relation to Senescene Characteristics of Sorghum

The stems remaining after harvest of sorghum [Sorghum bicolor (L.) Moench] grain are a low‐cost source of biomass. Semidwarf hybrids exhibiting nonsenescent characteristics may yield more stem biomass than senescent hybrids. This study compared a nonsenescent to a senescent hybrid of semidwarf sorghum using dry wt. and partitioning of 14C‐photosynthate and 14C‐starch at three stages. A leaf was exposed to 14CO2 or 14C‐starch was injected into the middle internode of each hybriduring grain filling and at or after (post) black layer of the grain. Although dry wt. of stem internodes were significantly (P ≤ 0.05) greater for the nonsenescent compared the senescent hybrid, 14C‐photosynthate partitioning among parts did not differ between hybrids after chase periods of 5 or 7 d. Patterns of 14C‐photosynthate partitioning indicated grain, stem internodes, and lateral branches were dominant sinks at grain filling, black layer, and post black layer, respectively. Lateral branch growth comprised all of the biomass increase from black layer to post black layer. At post black layer, 47% of assimilated 14CO2 was partitioned to lateral branches. Both 14C‐photosynthate and 14C‐starch were remobilized from stem internodes to lateral branches of both hybrids after black layer. Although unmeasured in previous comparisons betweenonsenescent and senescent sorghum hybrids, lateral branch growth limited storage of 14C‐photosynthate in stem internodes and resulted in similar patterns of 14C‐photosynthate partitioning for the two hybrids after black layer in this study.