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Performance of a Winter Wheat Hybrid, F₂, F₃, and Parent Varieties at Five Population Levels¹

The F₁ and parents involved in a winter wheat cross (‘Reed’ X ‘Gaines’) were grown at five population levels under irigation for 3 years at Aberdeen, Idaho. The F₂ was grown in the same experiment for 2 years and the F₃ for 1 year.

A slight amount of heterosis was expressed in plant height.

Heterosis was expressed by the hybrid in grain yield. When means over all five population levels were compared, the F₁ produced more grain than either parent in all 3 years. Differences were significant except for that between the F₁ and Gaines in 1965. The F₁ produced significantly more grain than the F₂ in 1964 and 1965, and the F₃ in 1965. There was no significant difference between the F₂ and F₃ in 1965.

No heterosis was evident in number of spikes per plant. Gaines produced more spikes per plant than the hybrid each year. Some degree of heterosis was expressed in number of kernels per spike and in kernel size 2 years out of 3.

Reed (tall variety) was used as border around all plots in two replications and Gaines (short variety) was used as border in two replications in 1963 and 1964. The only significant competition effects measured were on height in 1964 and on grains of grain per plot in 1963. Each entry in 1965 was bordered by itself.

F₁ and parent plants were slightly taller when grown at the higher plant densities.

Population level had an effect on grain yield. In 2 out of 3 years highest yields were produced by the hybrid and by Gaines at level 3. In no year were the F₁ means at population levels 3, 4, or 5 significantly different. The same was true for both parents. On the basis of this test a producer could cut his seeding rate to that of population level 3 (approximately one plant per 2.5 cm (1 inch) or 0.9 hectoliter per hectare (3- pecks per acre). This could be important if hybrid wheat seed becomes available and is relatively costly. More tests at different population levels should be conducted before a general recommendation can be made.

Plants grown at low population levels produced more spikes and more kernels per spike than those grown at high levels. Seed size was little influenced by plant density, although there was a trend toward smaller seed at the high population levels.

Key Words: hybrid winter wheat • population level • yield • components of yield

² Research Agronomist, Crops Research Division, Beltsville, Md.; Biometrician, Biometrical Services, Beltsville, Md.; and Agricultural Research Technician, Crops Research Division. Aberdeen, Idaho, ARS, USDA.

Received for publication March 20, 1967.