Allelopathy Journal

Black locust (Robinia pseudo-acacia L.) is an invasive and non-native plant in Japan that has caused considerable changes in the ecosystem of some riparian and coastal forests of Japan. Heartseed walnut (Juglans ailanthifolia Carr.) is a native allelopathic species in Japan, China and Korea. It is thought to produce the allelochemical juglone (5-hydroxy-1,4-naphthoquinone) that could inhibit the growth of black locust. A quantitative analysis of juglone in the heartseed walnut was done and its allelopathic activity was determined as a potential means for biological control of black locust. The amount of juglone in the fresh root of heartseed walnut was 0.87%, although juglone amounts differed depending on the plant part and drying. Using sandwich method, roots of heartseed walnut drastically inhibited the growth of lettuce (78.3%), while, roots of R. pseudo-acacia and Bischofia javanica caused 61.9% and 42.2% inhibition in radicle elongation of lettuce, respectively. Heartseed walnut had the strongest allelopathic activity among other allelopathic plants tested. Total allelopathic activity (TAA) of heartseed walnut was 5000 (no unit) on the growth of lettuce and 2500 (no unit) on black locust, considerably higher than other allelopathic plants. The inhibitory activity of heartseed walnut root on the radicle growth of lettuce was explained by the juglone present in the crude extract.