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

The F₁ and parents involved in a spring wheat cross (‘Lemhi 53’ X ‘HenryX) were grown at five population levels under irrigation for 3 years at Aberdeen, Idaho. The F₂ was grown in the same experiment for 2 years and the F₃ for 1 year.

Little heterosis was evident in plant height.

Heterosis was expressed by the hybrid in grain yield. Performance of the F₁ compared to the higher parent was remarkably consistent. The F₁ produced 19.5% more grain (over all population levels) than the higher yielding parent in 1963; 19.2% more in 1964; and 16.5% more in 1965. In general, performance of the F₂ was lower than that of the F₁, and performance of the F₃ was slightly lower than that of the F₂.

The hybrid produced more spikes per plant than either parent, but no heterosis was expressed in number of kernels per spike. Limited heterosis was evident in kernel size.

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

Population level had a pronounced effect on yield of grain. An apparent maximum yield was reached by hybrid plants when spaced 1.27 cm ( inch) apart within rows which were spaced 30.5 cm (1 ft) apart. This represents a seeding rate of approximately 1.9 hectoliters/ha (6- pecks per acre). Yield was not significantly reduced, however, in 2 of the 3 years, when plants were spaced 2.54 cm (1 inch) apart. This is equivalent to a seeding rate of approximately .9 hectoliter/ha (3 pecks per acre). Cost of hybrid seed could force a producer to reduce his seeding rate to near the latter level. More yield trials of a similar nature are needed before a positive recommendation can be made. Yield of parents was likewise influenced by plant density but was more erratic from year to year than yield of the F₁.

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

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

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

Received for publication February 17, 1967.