Do More Seeds per Panicle Improve Grain Sorghum Yield?

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Seed number, rather than seed mass, is largely considered to be the most important yield component of grain sorghum [Sorghum bicolor (L.) Moench]. An experimental sorghum mutant line with enhanced seed number (tri‐seed) was grown at the Soil–Plant–Environment Research (SPER) facility, USDA–ARS, Bushland, TX, in 2014 and 2015 to provide field validation of the tri‐seed line's ability to increase yield. The SPER facility had a rain shelter to control the soil‐water balance. The parent inbred line BTx623 and the tri‐seed line MSD‐P5, which originated as a mutant of BTx623, were grown in weighing lysimeters with undisturbed soil profiles of four agriculturally productive soils (Pullman clay loam, Ulysses silt loam, Amarillo sandy loam, and Vingo fine sand) of the US Great Plains. Planting density was 16 plants m−2 and the crops received either 18 or 36 mm of irrigation weekly. The tri‐seed line produced significantly smaller grain yield, seed mass, and total biomass compared with the parent line. The mass per panicle was similar between lines, but a significantly larger proportion of the tri‐seed line panicle was non‐grain panicle mass compared with the parent line. Both hybrids exhibited some plasticity in seed mass to accommodate assimilate as it became available, but increased seed mass, along with increased seed number, also did not result in a significant increase in harvest index for the tri‐seed line compared with the parent line. The increase in seed number by the tri‐seed line did not compensate for the decreased seed mass, which consequently failed to increase grain yield or harvest index.