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Breeding Methodology in Wheat. I. Determination of Characters Measured on F₂ Spaced Plants for Yield Selection in Spring Wheat¹

Three crosses of spring wheat (Triticum aestivum L.) involving the cultivar ‘Glenlea’ as a common female parent were used to evaluate the use of physiological and/or morphological parameters alone or in combination on F₂ plants as selection criteria to identify high-yielding F₄ bulks. The F₂ generation was grown as spaced plants in the field under two types of environmental regimes: (1) a regime and (2) a normal regime. Stress-free plants were given regular irrigation, optimum fertilization and complete weed control to minimize stress while the normal-regime plants were given no special treatment. Two hundred plants of each cross were measured for physiological, morphological, yield-component, and phenological traits. A random sample of 50 seeds from each of these plants was used to generate F₄ bulks. For each cross, groups of 45 F₄ bulks derived from stress-free F₂'s and 75 F₄ bulks derived from normal F₂'s were tested for yield in the F₄ in a six-replicate, partially balanced lattice design.

The results indicated that single F₂ parameters which described source capacity, sink capacity or plant morphology all identified high-yield potential in the F₂; however, at 15% selection intensity only 17 out of 53 high-yielding F₄ bulks were retained. A multiple regression analysis was found to be better than a single parameter approach, retaining nearly half (24 out of 53) of the high-yielding lines. A combined-cross analysis indicated that yield, productivity, kernel number, peduncle length, and productivity per tiller were all significantly correlated with F₄ bulk yields. A multiple regression analysis of the combined crosses indicated that productivity and peduncle length were the only significant common parameters

Key Words: Triticum aestivum L. • Early generation selection

² Graduate student and professor, Dep. of Plant Science, Univ. of Manitoba, Winnipeg, Manitoba, R3T 2N2.

Received for publication October 9, 1979.