Author
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VAN ETTEN, MEGAN - University Of Michigan |
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Brunet, Johanne |
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Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/7/2015 Publication Date: 3/10/2017 Publication URL: http://handle.nal.usda.gov/10113/5695306 Citation: Van Etten, M.L., Brunet, J. 2017. Using population matrix models to reduce the spread of wild carrot. Acta Horticulturae. 1153:273-278. doi: 10.17660/ActaHortic.2017.1153.40. Interpretive Summary: Wild carrot is a weedy plant that has been declared invasive in North America. It was likely introduced as a weed from Europe, has spread since its introduction and is now present in every state. Plants of wild carrot tend to mate with one another; wild carrot is a high outcrosser with a high potential for gene flow and gene spread. It is pollinated by various insects, including bees, syrphids and flies. Plants of wild carrot can easily be crossed with plants of cultivated carrots and produce viable offspring known as hybrids. Hybrids share genes from both the cultivated and the wild carrot. Therefore, the introduction of a genetically modified cultivated carrot could create a high risk of gene transfer to wild carrot and the transfer of genes that confer any advantage to wild carrot could further increase its weediness and facilitate its spread. Such events would necessitate the development of effective strategies to limit the spread of wild carrot. Understanding the demography of wild carrots would facilitate the development of effective tools for control. It would permit the identification of life history stages that most affect the growth of wild carrot populations and hence methods of control could focuson these life history stages. In this study, we examined life history stages of wild carrots in Wisconsin. We gathered data on reproduction, germination rate, overwinter survival and flowering rate. . Carrot plants produced 4,402±484 seeds per plant and seed production did not vary between years or populations. Secondary umbels contributed 58% of the total seed production of a plant. Germination rate varied between years (2.7- 30.9%). Of the plants that germinated, 40.9% survived over winter and 6.3% of the survivors flowered. We used these life history and germination data in a model that permitted the study of the population dynamics of wild carrot. Population dynamics examines how the number of individuals in a population changes over time. We used a stage structure model for a biennial lifecycle. Because germination differed among years, we examined two models, one with low and one with high germination rate. Even with the low germination values, carrot populations were predicted to increase in size (' > 1), with a growth rate (') of 1.9 for the low germination and 6.1 for the high germination models. We identified overwinter survival of rosettes and flowering rate as the two life history stages that most affected population growth. Therefore, preventing the flowering of individuals and increasing the mortality of non-reproductive individuals would be the most effective methods of control against spread. It would be more effective than limiting the number of seeds produced or decreasing the germination rate. Therefore mowing strategies that prevent flowering would represent an effective strategy against the spread of wild carrot. Even in the low germination model, however, 1 flowering plant would give rise to 382 plants over three years so it is very important to mow all or most of the individuals before any of the umbels set seeds. Such information would benefit scientists and government officials interested in developing management strategies to help limit the spread of wild carrots. These strategies would become imperative if transgenes likely to increase the weediness of wild carrot were introduced into carrot cultivars. Technical Abstract: Wild carrot was likely introduced to North America as a weed from Europe. It has spread since its introduction, now occurs in every state and has been declared invasive. Because wild carrot can easily hybridize with cultivated carrots, is an outcrosser and is pollinated by various insects, the introduction of a genetically modified carrot could create a high risk of gene transfer to wild carrot. The transfer of genes that confer a selective advantage could further increase the weediness of wild carrots and necessitate the development of effective strategies to limit its spread. A better understanding of the demography of wild carrots would help identify the life history stages that most affect population growth, which in turn would permit the development of effective strategies to control its spread. In this study, we examined reproduction, germination rate, overwinter survival and flowering rate in wild carrot populations. We used the life history and germination data to parameterize a stage structure model for a biennial lifecycle. We examined the population dynamics of wild carrots and identified the life history stages with the largest impact on population growth. Carrot plants produced 4,402±484 seeds per plant and seed production did not vary between years or populations. Secondary umbels contributed 58% of the total seed production of a plant. Germination rate varied between years (2.7- 30.9%). Of the plants that germinated, 40.9% survived over winter and 6.3% of the survivors flowered. Even with the low germination values, carrot populations were predicted to increase in size (' > 1), with a growth rate (') of 1.9 for the low germination and 6.1 for the high germination models. The life history stages that most affected population growth were changes in overwinter survival and flowering rate. Therefore, preventing the flowering of individuals and increasing the mortality of non-reproductive individuals would be the most effective methods of control against spread and would be better than limiting the number of seeds produced or decreasing the germination rate. Such strategies would become imperative if transgenes likely to increase the weediness of wild carrot were introduced into carrot cultivars. |
