The effects of frequency and intensity of grazing on the genotypic structure of a ryegrass population

Abstract

An experiment is described in which changes in the genotypic structure of a short-rotation ryegrass population, as induced by different frequencies and intensities of grazing, were studied. The plant material was obtained from plants surviving from a sowing of short-rotation ryegrass and red and white clovers which had been subjected to four different grazing systems, and from single-spaced plants grown from the same seed. From observations made on morphological characters of the plants both in boxes and later in the field, changes in the original population were determined, for the different grazing systems. In terms of plant means, there was a selection within the original population 'towards the perennial ryegrass types under frequent and intensive grazing, and towards the Italian ryegrass types under the less intensive and long-spelled grazing systems. These trends were also shown in the genetic components of the plant variances. The results are discussed in relation to the rapidity of response to the management systems applied; to the adaptability of the species because of the large number of plants originally used as the genotypic basis of this synthetic strain; and to the species reaction to changing management systems. The use of simply inherited characters such as fluorescence and awning, for genecological studies in ryegrasses is also discussed.