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Genecological studies of groundsel (Senecio vulgar is L.)
Author(s) -
BRIGGS D.,
BLOCK M.,
FULTON E.,
VINSON S.
Publication year - 1992
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1992.tb01113.x
Subject(s) - outcrossing , weed , noxious weed , biology , population , geography , botany , agronomy , horticulture , demography , pollen , sociology
summary Plants of groundsel ( Senecio vulgaris L.) in the very well‐kept University Botanic Garden, Cambridge are quicker in their rate of development than those from sites subject to less regular or no weeding pressure. However, the directional selection pressure favouring precocity has not resulted in population uniformity. In order to generate hypotheses about the development and maintenance of population variation in this annual weed, we have studied the origin and patterns of migration of two genetic variants. Also, we have investigated the history of the oldest established flowerbeds in the Garden, with particular reference to continuity of use and garden practices. The Systematic Beds have been in existence for more than 140 years and, despite periods of difficulty, have been subject to regular and frequent weeding. Evidence suggests that the radiate variant of groundsel was most likely introduced into the Garden in the late 1890s from plants collected at Bandon Station, County Cork, Ireland. Subsequently, this plant ‐ var. hibernicus Syme ‐ spread to many parts of the Garden but it did not establish itself on the Systematic Beds until 1985. Using the radiate capitulum locus as a marker, our results reveal a consistently very low level of outcrossing in non‐radiate plants and a more variable and seasonally higher frequency in radiate plants. In 1987, simazine resistant plants were detected in the Systematic Beds, an area which has never been treated with triazine herbicides. It seems likely that these resistant plants originated from a population of resistant plants on treated ground just outside the western border of the Garden. Two models have been devised to explain our findings. The first model postulates that weeding has been too efficient on the Systematic Beds to permit the slower developing radiate plant to establish itself there. A second model, which appears to fit the facts more closely than the first, postulates that the migration of the radiate variant has been restricted by gene flow.