Skew distribution of panicle-emergence dates in populations of cock's-foot, Dactylis glomerata L. (Gramineae)

Abstract

The date distribution of emergence in panicles of Dactylis glomerata was studied over several years at the Welsh Plant Breeding Station, Aberystwyth. Indigenous populations from southwest England, and western France showed a negatively skew distribution, as did cultivars from U.S.A., Denmark, and New Zealand, but in those from U.S.S.R. the skewness was not significant. It is suggested that this negative skewness could have arisen as a selective response to light intensity. This could explain why the predominant growth forms in the species' natural habitat are of the taller ‘hay’ type. The method of growing seed commercially in drilled rows over many generations has eliminated the prostrate forms. The latter have survived in old pastures but never predominate, and may be greatly reduced should the intensity of grazing be increased and prolonged. Self regeneration by ‘own’ seed in sward plants is hindered by ‘Choke’ disease (Epichloe typhina) which inhibits and can prevent panicle emergence so that in extreme cases plants become vegetative and non-sexual. There seems to be no inherent physiological barrier to late heading, but it has not, so far, been possible to assemble a population of agronomically suitable late-flowering plants. For this reason breeders have not been able to produce cultivars of cock's-foot comparable with the late-heading, leafy, grazing varieties developed in Lolium perenne.