Duration and Inheritance of Leaf Initiation, Spike Initiation, and Spike Growth in Barley1

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Three preanthesis growth periods were studied in barley (Hordeum vulgare L.) in order to identify genetic variation and estimate heritability for the three periods. Duration of the three periods, leaf initiation, spike initiation, and spike growth, was determined in a field experiment by dissecting and observing shoot apices. In a comparison of 10 cultivars, mean duration of the leaf initiation, spike initiation, and spike growth periods was 10.2, 9.6, and 20.6 days, respectively. Genetic diversity was found for each of the three periods with cultivar means ranging from 4.9 to 13.6, 7.3 to 12.2, and 17.1 to 23.5 days. Cultivars with similar duration of the vegetative period exhibited modest but significant differences in duration of the three periods. Cultivar means for rate of spike initiation ranged from 1.8 to 2.5 nodes per day; these differences were not significant. Duration of leaf initiation was correlated with leaf number; duration of spike initiation with leaf area, spikelet primordia number, and kernel number; and duration of spike growth with leaf area, height, spikelet primordia number, spikelet primordia survival, and kernel number. Parent‐offspring heritability estimates were 0.43, 0.60, and 0.68 for duration of the leaf initiation period in three segregating populations. Inconclusive evidence was obtained for a major gene affecting duration of the leaf initiation period in two of the three populations. Genetic variation was nonsignificant for duration of the spike initiation period in the three populations and heritability estimates were not different from zero. Estimates of heritability for duration of the spike growth period were 0.59, 0.23, and 0.74. The correlations involving leaf and kernel number with duration of two of the growth periods indicate possible benefits from breeding for optimum duration. While conjecture on the optimum duration of the three growth periods is probably not warranted, genetic variation in duration of the growth periods might be used in breeding for increased yield via obtaining durations better suited to specific environments.