Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/1999
Publication Date: N/A
Interpretive Summary: Invasive weeds pose a threat to native plant communities. Garlic mustard, a biennial forest understory herb which was introduced from Europe, has spread rapidly through much of the eastern half of the U.S. and Canada. Garlic mustard displaces native plants, and also appears to negatively impact insects, small mammals, ground nesting birds, and amphibians, therefore reducing biodiversity in infested areas. Attempted control using prescribed fires, hand weeding, and use of herbicides have been successfully employed to control small populations but are expensive and labor-intensive and have not resulted in long-term control of larger populations. In its native range, garlic mustard occurs in relatively small populations, unlike what is found in North America. Biological control utilizing specialized pests of garlic mustard, while not eradicating the plant, can significantly reduce the plant's impact. However, before specialized pests are introduced, it is necessary to understand why garlic mustard can dominate these understory ecosystems. We have found that garlic mustard tissues contain potent phytotoxins which can inhibit the germination and growth of neighboring plants. The information obtained in this study will assist scientists in developing control methods for garlic mustard in the U.S.
Technical Abstract: Several phytotoxic hydrolysis products of glucosinolates, principally allyl isothiocyanate (AITC) and benzyl isothiocyanate (BzITC), were isolated from dichloromethane extracts of garlic mustard [Alliaria petiolata (Bieb) Cavara & Grande]. AITC and BzITC were much more phytotoxic to wheat (Triticum aestivum L.) than their respective parent glucosinolates sinigrin and glucotropaeolin. However, garden cress (Lepidium sativum L.) growth was inhibited to a greater degree by glucotropaeolin than BzITC, possibly due to conversion to BzITC by endogenous myrosinase. Sinigrin and glucotropaeolin were not detected in leaf/stem tissues harvested at the initiation of flowering, but were present in leaves and stems harvested in the autumn. Sinigrin levels in roots were similar for both sampling dates, but autumn-harvested roots contained over three times higher glucotropaeolin than spring-harvested roots. The dominance of garlic mustard in forest ecosystems may be attributable in part to release of these phytotoxins, especially from root tissues.