Occurrence of Juglone in Various Tissues of Pecan and Related Species

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Abstract
Measurements of the seasonal distribution of juglone (5-hydroxy-1,4-naphthoquinone) among various tissues of pecan (Carya illinoensis ''Van Deman'') [involved in resistance to Cladosporium caryigenum] among various tissues of pecan (Carya illinoensis ''Van Deman'') revealed that the highest concentrations occurred in the leaflets in June but in the nuts in September. The leaf rachis, twigs, twig bark, trunk, root, and root bark had lower concentrations at both dates. Therewere no changes in juglone content of twigs sampled at monthly intervals or differences among twigs of five pecan cultivars at any date. Very little juglone was detected within pollen of several hickories (including pecan). The concentration of juglone in husk, kernel, and leaflet of black walnut (Juglans nigra), shagbark hickory (Carya ovata), and four pecan cultivars were: in husks, walnut > history and pecan; in leaflets, walnut > pecan and hickory: and in kernels, walnut > hickory > pecan. Seedlings grown in greenhouse pots and girdled to the cambium had a higher concentration of juglone in the leaves than did nongirdled seedlings, suggesting that juglone was synthesized in the leaf area and translocated by the phloem.