Heterosis and Combining Ability in a Diallel Cross of Onions1

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Abstract
Nine inbred onion (Allium cepa L.) lines of diverse origin and known horticultural performance were crossed in diallel to measure the extent of heterosis for yield and 6 other traits and to evaluate the types of gene action involved in character expression. Parents and the 36 F1 hybrids were compared at 2 locations (Michigan and Wisconsin) in 1975. Average performance of the parents and hybrids showed good agreement between environments for yield and several other traits. The mean performance of F1 hybrids fell within the range of parents for all characters. Although not always significant, F1’s on the average yielded more, were earlier to mature, had greater bulb weights, more centers, fewer rings, and were less firm than the average of the better parents in crosses. Heterosis was significant and favorable at both locations for yield, maturity, and bulb weight, but unfavorable for centers/bulb. Yield heterosis of the hybrids over the mid- and high parent, respectively, were 39 and 20% at Palmyra, Wisconsin and 27 and 12% at East Lansing, Michigan. In general, high F1 yields were associated with crosses involving high yielding parents. Variances of general combining ability (GCA) predominated for all traits. Small but significant specific combining ability (SCA) effects were noted for maturity, bulb firmness, and % of storage loss.

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