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Genetic Control of Spikelet Number in Hexaploid Wheat¹

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 x 8–27) x 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.

Key Words: Grain yield • Developmental response • Quantitative inheritance • Breeding

² Postgraduate student, senior lecturer, and reader respectively, School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria 3052, Australia.

Received for publication June 7, 1976.