Studies on Growth and Development in Lolium: III. Influence of Season and Latitude on Ear Emergence

Abstract

This paper relates local and seasonal variations in ear emergence of L. perenne to local and seasonal differences in photoperiod and spring temp. within the British Isles. This involves (1) a study of ear development under controlled temp. and photoperiod; (2) the collection of ear emergence data from transplant material over a range of latitude and spring temp. Most plants of L. perenne become able to respond to photoperiod only after exposure to low temp., usually obtained by overwintering outdoors. The amount of low temp. exposure required varies from strain to strain. Ear initiation in response to photoperiod occurs in the early-flowering strains by late Feb. with a photoperiod of 11-12 hours, in the late-flowering strains by early April with a photoperiod of 13-14 hours. After the photoperiodic threshold has been reached, rate of ear development is influenced mainly by spring temp. Records from transplant centers show a geographical trend from early-flowering in s.-w. Britain to late-flowering in the north-east, but this trend is modified by altitude. Although ear emergence is strongly influenced by season and locality, the relative order of early and late-flowering strains remains the same. Genetic variation in ear emergence is of the same order as environmental variation. The effects of both locality and season are explicable in terms of spring temp. after the critical daylength has been reached.