AOBPreview originally published online on April 15, 2004
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Annals of Botany 93: 653-663, 2004
© 2004 Annals of Botany Company
Ecological Genetics of Vernalization Response in Bromus tectorum L. (Poaceae)
1 USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, Provo, Utah, USA
* For correspondence. E-mail: smeyer{at}fs.fed.us
Received: 20 February 2003; Returned for revision: 7 May 2003; Accepted: 29 January 2004; Published electronically: 15 April 2004
• Background and Aims Bromus tectorum (cheatgrass or downy brome) is an exotic annual grass that is dominant over large areas of former shrubland in western North America. To flower in time for seed production in early summer, B. tectorum plants generally require vernalization at winter temperatures, either as imbibed seeds or as established seedlings.
• Methods Variation in response to increasing periods of vernalization as seeds or seedlings for progeny of ten full-sib families from each of four B. tectorum populations from contrasting habitats was studied.
• Key Results As vernalization was increased from 0 to 10 weeks, the proportion of plants flowering within 20 weeks increased, weeks to initiation of flowering decreased, and seed yield per plant increased, regardless of whether plants were vernalized as seeds or seedlings. Most of the variation was accounted for by differences among populations. Plants of the warm desert population flowered promptly even without vernalization, while those of the cold desert, foothill and montane populations showed incremental changes in response variables as a function of vernalization period. Populations differed in among-family variance, with the warm desert population generally showing the least variance and the cold desert population the most. Variation among populations and among families within populations decreased as vernalization period increased, whereas the non-genetic component of variance showed no such pattern.
• Conclusions Variation in vernalization response was found to be adaptively significant and apparently represents the result of contrasting selection regimes on a range of founder genotypes.
Key words: Bromus tectorum, cheatgrass, chilling, downy brome, ecological genetics, flowering phenology, reproductive output, vernalization, winter annual.
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