ABSTRACT
The severity of infestations of Canada thistle (Cirsium arvense (L.) Scop.) can be predicted by determining the potential of its root system to expand and produce new shoots. The root systems of young and old plants of Canada thistle were observed under field conditions found in Alberta. Eighteen-week-old plants grown in 1985 and 1986 had an average of 26 aboveground shoots, 154 underground shoots, and 111 m of roots with a diameter larger than 0.5 mm. The number of root buds and the regenerative capacity of the roots varied between years. Four times as many nonemerged root buds per meter of root were present on plants grown in 1986 compared to 1985, and 50% more shoots per meter were produced from 10-cm-long root fragments collected from 18-wk-old plants in 1986 than in 1985. On average, an 18-wk-old plant had the potential of producing 930 shoots if its root system was cut into 10-cm-long pieces. The depth reached by roots in a 10-yr-old stand was about 2 m, with the major part of the root system being below the top 20 cm of soil. There was no correlation between the number of root buds present at sampling time and the number of shoots produced from root fragments planted in pots in the greenhouse. An average of eight shoots per meter of root was produced, irrespective of sampling depth.Key words: Canada thistle, Cirsium arvense, root buds, root system, regenerative capacity
ABSTRACTThe severity of infestations of Canada thistle (Cirsium arvense (L.) Scop.) can be predicted by determining the potential of its root system to expand and produce new shoots. The root systems of young and old plants of Canada thistle were observed under field conditions found in Alberta. Eighteen-week-old plants grown in 1985 and 1986 had an average of 26 aboveground shoots, 154 underground shoots, and 111 m of roots with a diameter larger than 0.5 mm. The number of root buds and the regenerative capacity of the roots varied between years. Four times as many nonemerged root buds per meter of root were present on plants grown in 1986 compared to 1985, and 50% more shoots per meter were produced from 10-cm-long root fragments collected from 18-wk-old plants in 1986 than in 1985. On average, an 18-wk-old plant had the potential of producing 930 shoots if its root system was cut into 10-cm-long pieces. The depth reached by roots in a 10-yr-old stand was about 2 m, with the major part of the root system being below the top 20 cm of soil. There was no correlation between the number of root buds present at sampling time and the number of shoots produced from root fragments planted in pots in the greenhouse. An average of eight shoots per meter of root was produced, irrespective of sampling depth.Key words: Canada thistle, Cirsium arvense, root buds, root system, regenerative capacity
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