Analysis of Variation in Growth Habit of Lolium Populations

Genetic variation in growth habit between six contrasting populations of Lolium perenne and L. multiflorum is analysed by means of a complete diallel grown in three seasonal environments. The main population differences are between the more erect biennial forms of L. multiflorum and the prostrate perennial forms of L. perenne. It is suggested that these differences are attributable to past agronomic (biotic), rather than climatic, selection pressure. In winter all six parental populations are more erect than in spring or summer, although interaction between populations and environments does occur. The genetic control of the population differences is due to average zygotic effects but both constant and residual reciprocal effects of the parent also determine the performance of the F1 crosses over the three environments. Reciprocal effects are constant over environments, whereas average zygotic effects interact with environments.