Morphological and genetic variation within perennial ryegrass (Lolium perenne L.)

Perennial ryegrass (Lolium perenne L.) is a widely used forage species in temperate regions and BG34 is a commonly used cultivar blend composed of the cultivars Barlet, Barmaco, Barnhem, and Mara in various proportions. This research used perennial ryegrass as a model plant to (i) quantify within- and between-cultivar variation of L. perenne cultivar blend BG34 on the basis of several morphological characteristics and forage yield; (ii) examine the relative yield of L. perenne in response to genotypic diversity and how this response was affected by defoliation frequency and intensity; (iii) investigate the responses of production components i.e. tiller number, tiller weight, plant mass and survival of individual genotype, and how this was affected by the treatments of genotype and defoliation; and (iv) evaluate the suitability of SSR (simple sequence repeats) and ISSR (inter simple sequence repeats) markers to differentiate the cultivars of L. perenne that comprise BG34 and investigate the genetic structure of pastures sown with BG34 ryegrass from dairy fields in Ohio.; With 100 potted plants of the four cultivars investigated, within-cultivar variation accounted for 73--97% of the total variation for the morphological traits (i.e. height, tiller number, erectness, leaf width and yield). Measurement of cloned plants found 13.4 to 89.9% of the variation could be attributed to genetic variation depending on traits. It was concluded that although there was morphological variation between these cultivars, it was smaller than the within-cultivar variation. It was predicted that the total variation of a mixture of these cultivars (e.g. as in BG34) would result predominantly from within-cultivar variation rather than between-cultivar variation.; The relative herbage yield of monocultures and mixtures of different genotypes of L. perenne was evaluated using cloned plants. Eight genotypes were selected, that were a factorial combination of four yield potential levels, and two tillering potentials. Genotype treatments were composed of one, two, four and eight genotypes per plot and the defoliation treatments were frequency (cutting interval of 3 week vs. 6 week) and intensity (cutting height at 20 mm vs. 60 mm). The data showed a significant linear relationship between genetic diversity and production and a significant difference between mono-genotype and multi-genotype treatments. The highest yielding treatments had only one genotype or two genotypes, yet their yield was not significantly higher than that of the complex mixtures with eight genotypes. Defoliation frequency and height had significant effects on forage yield. Frequent (3-wk) defoliation reduced grass yield by 12.7%, while the 60 mm height clipping reduced grass yield by 14.3%. It was concluded that genotypic diversity helped increase herbage yield and this response was modified by defoliation patterns. (Abstract shortened by UMI.)...