ALLELOPATHIC POTENTIAL OF ANTHOXANTHUM-ODORATUM FOR INVADING ZOYSIA-GRASSLAND IN JAPAN

The growth of Zoysia japonica surrounding Anthoxanthum odoratum on Zoysia-grassland in Japan was investigated in June 1990. The stem density of Z. japonica tended to decrease with short distances between two A. odoratum plants. This showed that the growth of Z. japonica surrounding A. odoratum was reduced. Basic, neutral, and acidic fractions extracted from A. odoratum plants inhibited the seedling growth of lettuce. In particular the neutral fraction showed the strongest activity among the three fractions. The main inhibitory compound obtained at R(integral) 0.6-0.7, on the thin-layer chromatogram of the neutral fraction, was isolated and identified as coumarin by means of GC-MS. Coumarin solution inhibited seedling growth of Z. japonica in low concentrations but, conversely, promoted seedling growth of A. odoratum. Coumarin was contained in all parts of A. odoratum and its concentration varied with the season and from one individual plant to another. In particular, coumarin was highly concentrated in the leaves, accounting for more than 2.5% of dry leaf weight in June. The inhibitory effect of these aqueous extracts was correlated to the amount of coumarin in A. odoratum leaves and coumarin was considered to be the main inhibitory compound.