Phloem Zinc Accumulation in Citrus Trees Affected with Blight1

Abstract

Abstract Zn content was higher in trunk bark (cambium to outer scrapings) than in the adjacent wood in healthy and blight-affected sweet orange (Citrus sinensis (L.) Osb.) and grapefruit (C. paradisi MacF.) trees. Zn levels were elevated in trunk bark and wood of blight-affected trees on rough lemon (C. limon (L.) Burnt, f.) rootstock, whereas affected seedling trees or trees on ‘Cleopatra’ mandarin (C. reticulata Blanco) rootstock that were tested had high Zn levels only in the bark. Bark Zn content was much higher above the bud union than below in blight affected trees on rough lemon or trifoliate (Poncirus trifoliata (L.) Raf.) rootstocks, but Zn content was high above the bud union in healthy trees only on rough lemon rootstock. The inner half of the bark, an area representative of the active secondary phloem, had much more Zn than the outer half of the bark or the most recently developed xylem. The outer half of the bark served as a barrier against outside contamination. Accumulation of Zn in wood occurred only when the phloem Zn was high.