Mature plant characters and yield components were measured on a two-row (Proctor) and a six-row (Clermont) spring barley variety, the F1 of the cross between them, and the first back-cross to each parent.
Whereas shoot dry weight in the F1 significantly exceeded the mid-parental value, and chaff dry weight, stem length and weight per grain showed positive heterosis, grain yield did not exceed the mid-parental value and number of grains per plant showed negative heterosis.
A scaling test showed that an additive-dominance model fitted the data in all cases except possibly for dry weight per grain, where the χ2 test approached significance.
The partial dominance of the two-row allele (V) for grains set per rachis node exhibited in the mature ears of the F1 was not apparent at anthesis when all the lateral florets were found to have large, apparently normal stamens. However, the ratio of median to lateral grains set over all main shoot ears of the F1 was 1:0·21 with an average of six lateral grains per ear.
The results presented indicate that the factors determining total dry-matter production and grain yield are inherited in such a way that the restriction upon grain yield in the F1 is due not to a deficiency of dry matter but to a limited capacity of the plant to store dry matter in the form of grain. This may indicate some developmental interdependence in the expression of yield component characters.