The effect of grazing on the persistence of genotypes in a ryegrass population

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Abstract
Changes in the genotypic structure of a mixed Ruanui and Manawa ryegrass population were determined after application of three systems of grazing management fCoT 5 1/2 years. Under Lax grazing 96% of the surviving genotypes had awned seeds. indicating predominance of genotypes contained in the variety Manawa. Continuous grazing resulted in the predominant survival of genotypes contained in the variety Ruanui, only 12% having awned seed. An intermediate system of grazing led to the survival of genotypes similar to those in the Lax grazing system, 88% of the genotypes having awned seeds. Surviving genotypes with awned seed from the Continuous grazing had vegetative characteristics intermediate to those of Ruanui and Manawa ryegrass. Measurement of a range of vegetative and flowering characters of the surviving populations allowed assessment of the usefulness of these characters in genecological studies of Lolium populations under grazing. Correlations between thLse characters from the surviving genotypes and the grazing systems were determined by the predominance of one or other of the two varieties in the different grazing systems. In addition to probable developmental correlations, correlation, were obtained within the variety Manawa which could indicate linkage, pleiotropic effects, or incomplete introgression in the hybridisation of Lolium perenne and L. multiflorum involved in the breeding of Manawa ryegrass.