Necrosis of Major Roots in Relation to Citrus Blight. J. H. Graham, Assistant Professor, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, Lake Alfred 33850. L. W. Timmer, Professor, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, Lake Alfred 33850, and R. H. Young, Plant Physiologist, USDA, ARS, Orlando, FL 32803. Plant Dis. 67:1273-1276. Accepted for publication 31 May 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1273.

Necrosis of bark and wood of major roots (>1 cm diam.) was observed on sweet orange (Citrus sinensis) trees on rough lemon (C. jambhiri) rootstock affected by citrus blight. The number of lesioned roots increased as the tree canopy declined and as diagnostic symptoms of blight, zinc accumulation, and restricted water flow in the trunk wood developed. Fusarium solani was consistently isolated from necrotic roots but did not cause lesions when roots of rough lemon seedlings or field trees on rough lemon rootstock were inoculated. Roots of blighted trees may have been susceptible to infection by Fusarium as a result of xylem blockage in the trunk, canopy decline, and subsequent decrease in starch reserves in the tree.