Genetic Pollution

Ginseng Flower

Though ginseng can pollinate itself,
crossing with neighbors also occurs,
providing a way for maladapted genes to
enter natural populations if cultivated
plants are introduced nearby

CITES regulates the export of roots of natural, ‘wild’, unplanted and uncultivated populations of ginseng, as well as the export of roots of cultivated ginseng.   But ginseng exists in a wide variety of growing conditions, ranging from intensive cultivation under shadecloth (Ontario, Wisconsin, and British Columbia, being centers of this practice), to ‘woods grown’ in cultivated beds, to ‘wild simulated’.  These growing practices can blur the distinction between cultivated and ‘wild’ ginseng, resulting in many heated disagreements about how to regulate ginseng trade, but shedding very little light.

Those who do not understand the nature of genetics may wildly underestimate its importance in many ways.  For instance, some will claim there is ‘no such thing’ as a wild ginseng population (all of them were planted by somebody!).  Others will advocate broadcasting seeds (inevitably from shade-grown cultivated plants) from helicopters to restore ginseng populations across the forest, not recognizing that there may be critically important genetic differences between wild andshade-grown cultivated seed sources.

Science has begun to shed some light on these issues.  First, using modern genetic tools, we now know that most ‘natural’ populations are not contaminated with genes from cultivated seed sources.1,2,3,4  Thus, claims that all populations are unnatural are clearly false.  Second, experiments have shown that crosses between plants from cultivated and wild seed sources are possible (they have not yet become separate species), and produce genetically distinct offspring.5  No one has yet examined whether such crosses introduce maladaptive* genes into natural populations, but there is every reason to believe that in theory, they could – the traits under selection in cultivation (rapid growth, ability to grow quickly in response to nutrient additions, low defenses against herbivory and fungal diseases) are precisely the wrong traits to allow persistence in the wild.  Using the precautionary principle, which is the centerpiece of Aldo Leopold’s philosophy of conservation biology, we discourage mixing of gene pools of natural and cultivated seed sources. 

By the same token, ginseng has all the hallmarks of a locally adapted species,6 so we encourage those attempting wild simulated ginseng husbandry to use, wherever possible, local seed sources, to ensure success, and minimize genetic pollution. Wild simulated ginseng can potentially reduce the pressure on wild populations of American ginseng by increasing the supply of roots to meet the demands of the Asian market. Therefore, when local seed sources are used, wild simulated production can be a conservation tool.

maladaptive*- meaning ‘bad’ for the growth, survival, and reproduction of the ‘native’ plant.

References

1Schluter and Punja 2002
2Grubbs and Case 2004
3Schlag and McIntosh 2012
4Young et al. 2012
5Mooney and McGraw 2007
6Souther and McGraw 2011