Dormancy in reproductive vegetative buds in creeping perennials dominating the agricultural weed flora in Scandinavia

Sammanfattning: Dormancy, which is the inability to initiate normal growth under otherwise favourable conditions, is an adaptation to escape sprouting prior to seasonal cold temperatures and/or drought in areas where winters are harsh or summers dry. Dormancy in woody perennials of northern temperate areas is, in general, induced by photoperiodic and/or temperature changes, and released after prolonged exposure to chilling. Besides being species specific, northern ecotypes are usually more sensitive to inductive signals than are southern ecotypes (in cold temperate areas). Dormancy in perennial weeds has been little studied, but might influence the effect of weed control measures. These often involve repeated fragmentation of the roots or rhizomes to stimulate re-sprouting, thus reducing the storage of nutrient reserves. Such measures would be a waste of energy and time if conducted during a period of dormancy. Furthermore, herbicide applications might be less efficient, since there is no or little transport to reproductive organs. In this thesis, the autumnal growth pattern of five perennial weeds, which all propagate vegetatively from underground adventitious or axillary buds, has been studied. In an outdoor pot experiment, emergence from defoliated plants with undisturbed underground systems was followed at two weeks intervals from late July to late January/April, for 2 years. During the second year, sprouting capacity from root and rhizome fragments was also tested. Emergence was impaired in Cirsium arvense, Equisetum arvense, Sonchus arvensis and Tussilago farfara during a period in September-October. This seasonality was, however, not preserved in C. arvense root buds after fragmentation of the root system. Fragmented rhizomes of Elytrigia repens, originating from southern Sweden, sprouted less readily in September-October. The shoot-to-rhizome ratio of this species was lowest during the same period. A climate chamber experiment suggested a photoperiodic control of sprouting from fragments of S. arvensis, with least sprouting in short photoperiods (12 h of light) combined with high temperature. None of the 12 combinations of photoperiods and temperatures used induced dormancy in C. arvense. In neither of the experiments could timing of dormancy onset be attributed to the latitudinal origin of the plants.

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