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Tillering Relationships Between Spaced and Densely Sown Populations of Spring and Winter Wheat¹

The relationship between tillering in space-planted early generation populations and in close-planted commercial-type stands of wheat (Triticum aestivum L.) was investigated over a 5-year period. The primary objective was to determine if this relationship is strong enough to justify selection for tillering type in spaced populations. Secondary objectives were to examine tillering- yield relationships and possible differences in tiller survival among wheat genotypes. Four winter and two spring wheat cultivars with known tillering differences in densely-seeded stands maintained their relative rankings when grown in spaced plantings. However, when F₅ plants selected for high or low tillering in spaced populations were subsequently grown in densely-sown F₆ plant-rows, little relationship was observed between tillering characteristics in the two planting densities. In attempting to explain the divergent results it is theorized that tillering differences among the cultivars, which had exhibited these differences over many years and environments, were largely genetic and would, therefore, likely persist regardless of planting density. Conversely, we suspect that much of the tillering variation observed among the spaced F₅ plants was non genetic and would lack consistency under dense seeding. The relationship between tillering in spaced and close plantings appears to be further complicated by the differential ability of genotypes to mature spike-bearing tillers, as a percentage of total tillers initiated. The cultivars we studied veried widely in the efficiency with which they matured fertile tillers in dense plantings. In only two of eight crosses did we observe a significant association between degree of tillering in space-planted F₅'s and in their densely-seeded F₆ plant-rows. Consequently, tillering differences in space-planted early generation wheat populations do not appear to provide a reliable selection criterion. We observed no consistency between grain yield and degree of tillering. Other yield components largely compensated for variation in tiller number, with kernels per spike having a greater effect than kernel weight.

Key Words: Triticum aestivum L. • Selection • Early segregating generations • Environmental effects • Small grains

² Professors of plant breeding, Dep. of Plant Science, Utah State Univ., Logan, UT 84322.

Received for publication June 4, 1984.