Genetic Variation in Potential Kernel Size Affects Kernel Growth and Yield of Sorghum

Large-seededness can increase grain yield in sorghum [Sorghum bicolor (L.) Moench] if larger kernel size more than compensates for the associated reduction in kernel number. The aim of this research was to investigate kernel filling characteristics associated with the high kernel weight of KS115 germplasm and consider implications for grain yield improvement. Germplasm with a twofold range in potential kernel size was grown in two field experiments. In both experiments, a large-seeded hybrid based on KS115 yielded significantly more grain than a normal-seeded hybrid with the same female parent. Genotypic differences in final kernel weight were associated with both an increased rate and extended duration of kernel filling. A high kernel filling rate was associated with a high rate of increase in kernel water content and kernel volume, which resulted in large maximum water content and volume per kernel. The long kernel filling duration of KS115-based germplasm was associated with an extended duration of the period of rapid water uptake into the kernel following the onset of rapid dry mass accumulation in the grains. For this particular germplasm, this was likely due to the presence of large ovaries before fertilization. Because of a trade-off between potential kernel weight and number, prolonged duration, rather than an increased rate of kernel filling, appeared to be the main mechanism through which large-seededness of KS115 could increase grain yield.