Manifestations of Hybrid Vigor in Grain Sorghum and the Relations Among the Components of Yield, Weight per Bushel, and Height1

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Abstract
One hundred and ninety grain sorghum hybrids, produced by crossing 10 male‐sterile lines with 19 fertility restorers, were compared with their parents over 2 years at Lincoln, Nebraska. The hybrids average 20% higher in grain yield, 0.5 lb. heaver in weight per bushel, 4.5 inches taller, and 2.5 days earlier than the mean of the parents. The yield advantage of the hybrids resulted mainly from increases in nmnber of seeds per head and, to a lesser extent, from increases in seed weight. Heterosis for yield was not expressed as increased tillering.The slight increase in weight per bushel resulted front slightly greater heterosis for seed weight than for seed volume.The hybrids were taller than their parents because they had longer stems, peduncles, and heads. Heterosis for stem length was manifested in the length rather than the number of internodes. It seems that the factors controlling the number and length of internodes differ from those determining peduncle and head lengths.The grain produced by the hybrids averaged lower in protein content than that produced by the parents. However, because of their higher yield, the hybrids averaged 16% higher than the parent in crude protein per acre.

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