Flowering Behaviour of Populations of Dactylis glomerata Under Field Conditions in Britain

Abstract

Recent investigations have shown that photoperiod is the most significant environmental factor controlling reproductive development in Dactylis glomerata (Calder 1963b, 1964). This grass exhibits at least three stages of development: a juvenile stage during which it is insensitive to photoperiod or low temperature; an inductive stage when short-day treatment leads to complete induction or the state of ripeness to flower (for the purposes of induction in Dactylis a photoperiod of 17 h is still effectively a short day, or in other words, Dactylis requires a minimal dark period in the diurnal cycle of something less than 7 h); and a post-inductive stage when the plant responds to long days and heads most rapidly in continuous light (Calder 1963a). This paper is concerned with the reproductive behaviour of a number of populations of D. glomerata grown under uniform field conditions at Aberystwyth (lat. 521' N, long. 4? W). The results are discussed in the light of our recent findings on the environmental control of flowering in this grass and on the reported flowering behaviour of Dactylis populations grown elsewhere. D. glomerata, a native of Europe, temperate Asia and North Africa (Beddows 1959), has been introduced as a forage grass into most temperate countries of the world. The species is composed of a number of populations adapted to very diverse climatic, edaphic and agronomic habitats. The genus Dactylis can be subdivided into a number of taxa, but most authorities include all the forms in the one species D. glomerata, although Borrill (1961b) has recently described a second species (D. marina). Within D. glomerata about thirteen subspecies have been recognized, eleven of which are diploid (Stebbins & Zohary 1959) and two tetraploid. Of the tetraploids, ssp. hispanica is a Mediterranean type of little agronomic importance, while ssp. euglomerata, which has given rise to practically all the cultivated varieties, has a more northerly distribution. Of the diploids only ssp. lusitanica from western Portugal appears likely to be useful in agriculture in Great Britain (Borrill 1961a).