Screening of allelopathic invasive plants in Japan and East Asia

Yoshiharu FUJII
Tokyo University of Agriculture and Technology, Tokyo, Japan

Exotic plants threaten the integrity of agricultural and natural systems throughout the world. Many invasive species are not usually dominant in their native regions, but once they invaded into new regions, they competitively suppress the growth of their new neighbors. Callaway and his colleague published many papers demonstrating the importance of allelopathy of dominating invasive alien plants in North America and coined "Novel weapons hypothesis" (Science 2000). We have developed specific bioassay systems for allelopathy, named "Sandwich Method", "Plant Box Method", and "Dish-pack Method". By using these methods, we have done screening in Japan and surrounding countires and found some of the invasive plants are allelopathic. Some of allelochemicals were isolated. Among these plants, several examples of allelochemicals from alien plants in Japan will be demonstrated:

1) Leucaena leucocephala: an invader to tropical and subtropical island has an unusual amino acid, mimosine, isolated as the major allelochemical in this leguminous tree;

2) Bishofia javanica: native to south east Asia, but now becoming an invader in Ogasawara Island, has tartaric acid as allelochemicals;

3) Prosopis juliflora: leaching of the allelopathic substance, L-tryptophan from the foliage of this mesquite was demonstrated. Juliflorine, a unique alkaloid, was also detected as major allelochemical;

4) Other invasive alien plants with potent allelopathic activity are: Coccinia grandis, Rottboellia cochinchinensis, Fumaria capreolata, Phalaris brachystachys, Physalis angulata, Gypsophila paniculata, Oenothera hookeri, Trifolium incarnatum, Ipomopsis rubra, Silene armeria, Avena strigosa and, Anisantha madritensis. Estimation of their invasion and toxicity to the environment, and the potential allelochemicals will be discussed. We would like to have cooperative research on the screening of allelopathic plants from East Asian Flora.

© 2012 Organizing Committee