VIEW ARTICLE

Cytology and Histology

Nature and Location of Xylem Blockage Structures in Trees with Citrus Blight. M. Cohen, Institute of Food and Agricultural Sciences, University of Florida, Agricultural Research Center, Fort Pierce 33454; R. R. Pelosi(2), and R. H. Brlansky(3). (2)Institute of Food and Agricultural Sciences, University of Florida, Agricultural Research Center, Fort Pierce 33454; (3)Agricultural Research and Education Center, Lake Alfred 33850. Phytopathology 73:1125-1130. Accepted for publication 28 February 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1125.

The relation of hydraulic conductivity to incidence of plugging in xylem vessels was studied in citrus trees with blight. Wood disks were cut from trunks, scaffold limbs, and large roots of cultivar Valencia orange trees on three rootstocks. Pegs, punched out along the diameter of the disks, beginning 0.5 cm inside the cambium and thereafter at 2-cm intervals, were used for conductivity measurements and for determination of numbers of vessel plugs present. In healthy trees conductivity was high and incidence of plugging low except near the pith. Trees with blight disease had high conductivity and little plugging near the cambium, but there was low hydraulic conductivity and much plugging in older xylem tissue. Amorphous plugs were dominant across most of the cross section of blighted trees and appeared to be the characteristic blockage structure found in trees with blight. Filamentous plugs were found mainly near the pith. Conductivity of twigs and pencil-sized roots from healthy and diseased trees was very similar, but vessel plugs were seen almost exclusively in twigs and roots from trees with citrus blight.