Intergenotypic Competition Between Tall and Dwarf Wheats. II. In Hybrid Bulks1

Abstract

Intergenotypic competition was studied in populations developed from a hybrid of two wheats (Triticum aestivum L. em. Thell.), ‘D6301’ (short‐statured) and ‘Ramona 50’ (standard‐height). The F2 through F6 generations were grown in the field in two replicate subpopulations without artificial selection. Heights of individual plants, taken from the F3, F4, F5, and F6 bulk populations, were studied in the same environment. Mean height increased and frequency of short‐statured plants decreased markedly from F3 to F6. Height of 62 random lines isolated from each of the F2, F4, and F6 generations showed a decrease in phenotypic variance from F2 to F6. Grain yields of the F2, F4, and F6 bulk populations and the means of 62 random lines (in F3, F5, and F7) indicated a significant increase from the F4 to F6 and from the F5 to F7 generations. At F7 the yield of the bulk population equalled the yield of the lower‐yielding parent, Ramona 50. Variance in yield among lines increased from F3 to F7, but extremely short genotypes did not appear in the F7. Extremely tall genotypes yielded less than those of intermediate height. Thus, in the bulk population directional and stabilizing selection affected both yield and plant height. Some lines in the F7 had higher yields than either parent. Thus, in spite of natural selection against the agronomically desirable short plants, the bulk populations were useful as source materials in selection for increased grain yield.