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A Comparison of Histochemical Staining Reactions of the Xylem Occlusions in Trees Affected by Citrus Blight and Declinio. M. J. G. Beretta, Plant Pathologist, Instituto Biologico, CP 7119, 01000, Sao Paulo, Brazil. R. H. Brlansky, and R. F. Lee. Associate Professors, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Plant Dis. 72:1058-1060. Accepted for publication 25 July 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-1058.

Declinio of citrus trees in Brazil, a vascular disorder of unknown cause, is similar to citrus blight in Florida. Both diseases are characterized by zinc accumulation in trunk wood and xylem plugging, which results in restricted water flow in diseased trees. This dysfunction is caused by the presence of xylem plugging. Amorphous and filamentous occlusions have been detected and reduced water flow has been correlated with amorphous plugs. The histochemical staining reactions of plugs found in xylem vessels in trees with declinio and blight were compared. With both diseases, the amorphous plugs reacted positively for callose, lignin, pectic substances, gums, proteins, and lipids. Filamentous plugs stained positively for lignins, gums, proteins, and lipids. These results showed that similar xylem plugs (amorphous and filamentous) were found in both declinio and blight, but the two plug types differ in their chemical composition.

Keyword(s): sweet orange, young tree decline.