Ecological Genetics of Vernalization Response in Bromus tectorum L. (Poaceae)

Chilling out in cool locations

The presence of a single species over a wide area gives opportunities to study adaptation to different conditions within that area. Thus, Meyer et al. (Provo, Utah, USA, pp. 653�663) work with a grass, Bromus tectorum, an invasive species now dominant on tens of millions of hectares of former cold desert shrubland and of sagebrush steppe vegetation. The extent of this range means that different populations are exposed to different climatic conditions and one of the authors� interests is to understand the adaptability of this species. In this paper, the focus is on vernalization, the need for exposure to a period of chilling in order to flower. Plants were collected from warm desert, cold desert, sub-montane and montane habitats and their vernalization requirements were determined. Vernalization at 2 �C was carried out on either imbibed seeds or established plants for up to 10 weeks. The authors obtained a large data set, of which we concentrate on the following. First, there was some correlation between the winter temperature of the plants� provenance and the vernalization requirement. Thus, the warm desert population flowered without any vernalization. In the other populations, some unvernalized plants flowered but the proportion that flowered was very markedly increased as the period of cold treatment was extended. Secondly, in the populations that exhibited a vernalization requirement, cold treatment of established plants was more effective than cold treatment of imbibed seeds. Indeed, with the montane population, even 10 weeks vernalization of seeds did not result in 100 % flowering. Thirdly, in all populations, even that from the warm desert, vernalization decreased the time to flower initiation. Finally, the authors note an earlier report showing that the warm desert population is represented by a singe genotype (as indicated by micro-satellite profile) whilst the other populations consist of several genotypes, providing evidence for genetic divergence resulting from habitat-specific selection.

Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk