Nature and Occurrence of Juglone in Juglans nigra L.1

Abstract Black walnut toxicity to crop plants was found to be due to the juglone (5-hydroxy-1, 4-naphthoquinone) in the tree (5). Cook (3) and Massey (9) suggested that toxic material came from the roots of the walnut tree. Bode (2) believed that the toxin came from the leaves. However, the quantity of juglone in the different parts of the walnut tree has not been fully established. Daglish (4) conducted experiments on Juglans regia , in which he suggested that juglone existed in the plant as glucoside of 1,4,5-trihydroxynaphthalene. On hydrolysis it yielded glocose and alpha-hydrojuglone.. This non-toxic hydrojuglone is oxidized to its toxic juglone from exposure to the air or some oxidizing substance from roots of other plants (6). Recent experimental data (Wang, unpublished) showed that 10 ppm commercially purified juglone reduced tomato seedling growth by 50 per cent when roots were immersed in the solution. A 100 ppm application killed the seedlings.