Mechanisms of frequency-dependent advantage in wheat

Abstract

The relationship between frequency-dependent advantage (f.d.a.) and competitive ability in wheat was investigated by growing F₁ hybrids and their parents in paired combinations at two frequencies, 6.25% and 25%. The results indicated that a strong competitor had an increased yield at a low frequency when grown in a stand of a weak competitor (thus exhibiting f.d.a.); however, the weak competitor was not significantly reduced when it was grown at low frequency. One hybrid (Warimek*Tirngalen) did not show f.d.a, when grown in either parent, which indicated that heterozygosity did not necessarily lead to f.d.a. The strong competitor, Timgalen, also showed f.d.a, in a mixture of other varieties, which suggested that the mechanism which resulted in f.d.a. in this genotype was specific to this genotype.

The physical basis of f.d.a, was studied in an experiment designed to permit assessment of relative competition for aerial and soil factors. The results indicated that f,d.a. was mainly associated with soil factors. Furthermore, there was a positive correlation between grain yield per plant and distance between the test plants, which suggested that f.d.a. was probably due to the interaction between roots of the same genotype in the exploitation of the environment in a slightly different way from that by other genotypes.

The significance of f.d.a, in the maintenance of genetic polymorphisms is discussed.