Dynamics of competition between wheat and oat: II. Effects of dwarfing genes

Previous studies in the United Kingdom (UK) and Australia have led to the hypotheses that reversals in competitive hierarchy between wheat (Triticum aestivum L.) and oat (A vena spp.) could occur only in situations in which (i) there is a reversal in the relative heights of the competitors during the year and (ii) there is strong competition for light. Reversals in competitive hierarchy should not, therefore, occur where the wheat is either taller or shorter than oat throughout growth. We grew near-isogenic lines of wheat for height in monoculture and in replacement mixtures with oat (A. sativa L. and A. strigosa Schreb.) in 2 yr. In the drier year and with a late-maturing oat cultivar, height of wheat had no influence over its competitive superiority, which was maintained throughout the season. In a somewhat wetter year and with an earlier-maturing oat cultivar, the shortest wheat lines were less competitive than corresponding taller near-isolines. Results were consistent for near-isogenic lines in three contrasting genetic backgrounds. Partial reversals in competitive hierarchy were seen in a late sowing, but these did not correspond with patterns in the relative height growth of the species.