Complementary competition in cultivated barley (Hordeum vulgare L.)

Summary Grain yield and its endpoint components were studied for three barley varieties, Dayton, Hudson, and Tenn 60-34, as pure stands and two-way and three-way mixtures at three widely separated sites for two years. The populations, including the pure stands, produced similar grain yields. Complementary competition was observed in all mixed populations in which Tenn 60-34 occurred. Its yield was suppressed in mixtures about 20% while Dayton and Hudson increased a like amount so that total mixed population yield was equal to that expected from pure stand performance. Tenn 60-34 occurred at 33, 50, and 80% frequencies in mixed populations with no difference in competition, indicating a lack of frequency dependency for the effect.Yield component data indicated that the reduced yield of Tenn 60-34 in mixed stands was due entirely to a decreased number of spikes produced per unit area. It was inferred that this was due to competition at time of tillering although this could not be determined since the varieties were indistinguishable during vegetative growth.An examination of population-environment interaction provided some evidence for the idea that heterogeneous populations in which there is intense competition show greater micro-environment (within-site) instability. Heterogeneous populations generally showed lower than expected contribution to the population-environment variance although the differences were quite small.These results have important implications for the utilization of heterogeneous populations in agricultural production and for the management of genetically diverse populations in plant breeding practice since genotypic frequencies are expected to change rapidly with complementary competition.