Genetic Control of Spikelet Number in Hexaploid Wheat1

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Abstract
Inheritance of spikelet number per ear was studied in wheat (Triticum aestivum L. em. Thell.) using the cultivar ‘Sunset’ and a land race cultivar ‘8–27’ under controlled temperature (20 C) and a photoperiod of (12 and 24 hours). Under the 24‐hour photoperiod, spikelet number per ear behaved as a quantitative trait in the F1 and F2 populations with indications of dominance for high spikelet number. However, the magnitude of environmental effects on the parents and F2 did not preclude the possibility of the F2 segregation being that of a single gene. The backcross F1 of the cross (Sunset ✕ 8–27) ✕ Sunset gave a 1:1 ratio for high:low spikelet number, indicating the likelihood of a single gene difference between these two wheats in the determination of spikelet number per ear. Under the 12‐hour photoperiod, however, low spikelet number was dominant and governed by a single gene which was most likely a gene governing a difference in photoperiodic sensitivity between the parents, and which masked the action of the gene governing differences in spikelet number. It is suggested that such studies be made under environmental conditions which minimize differences in the rate and/or duration of spike differentiation between the parents, revealing genetic differences in the expression. Alternatively, such studies may be conducted under any environments provided the parents have similar developmental patterns.