Mechanisms and genetic control of botanical composition in mixed swards

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Intraspecific genetic variability in relative competitive ability was examined in 15 cultivars of perennial ryegrass (Pr). The results were analyzed with the results obtained by previous studies of competitive experiments with orchardgrass (Og) and tall fescue (Tf) cultivars.(1) There were large differences in the relative proportion of biomass in the mixtures among the cultivars of the three grass species : 45-85% for Pr, 45-85% for Og and 11-43% for Tr.The results suggest that botanical composition in mixtures can be easily changed by genetic changes of populations.(2) There were close relationships between the relative proportion of the mixtures and tiller size in the monocultures in the three species.(3) However, the pattern and sign of their relationships varied with the species : a positive linear relation for Pr ; positive quadratic relation for Og and negative linear relation for Tf. I proposed the hypothesis that botanical composition of mixture swards is determined bythe balance between potential productivity and regrowth a bility after defoliation.