Conifers, seed development

Groth, E. (2010). Functional Diversification Among MADS-Box Genes and the Evolution of Conifer Seed Cone Development. Doctoral thesis, University of Uppsala. 

Development of weed resistance to triazine herbicides has necessitated alternative weed control strategies. Rotation of triazines with other herbicides and combining triazines with other chemistries has been effective in ornamentals and Christmas tree plantations (Van Himme, 1989). Supplemental treatments in Christmas trees have been effective, using directed sprays of phenoxy herbicides or glyphosate before resistant weeds mature and produce seeds. Weed resistance from triazines is not a problem in most forest settings where the herbicide is applied only once or twice in a rotation, since 1 or 2 years of herbaceous weed control normally ensures survival and eventual dominance by conifers. When the conifer canopy closes, virtually all herbaceous vegetation is shaded out for some decades hence resistant weeds, if present, fail to survive from one generation to the next. 

Having produced and selected a desirable strain, the breeder must then produce sufficient numbers of plants to test for trait stability and determine optimal conditions for commercial production. Unlike annuals that produce abundant seed, perennials with long generation times such as forest trees are a challenge to the plant breeder. For species such as conifers, advances in tissue-culturing techniques have transformed production processes in both the development and the marketing phases. 

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