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Cytology and Histology

Structural Comparison of Xylem Occlusions in the Trunks of Citrus Trees with Blight and Other Decline Diseases. R. H. Brlansky, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850; R. F. Lee(2), and M. H. Collins(3). (2)(3)University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Phytopathology 75:145-150. Accepted for publication 14 August 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-145.

Xylem occlusions were compared in citrus trees with blight (cause unknown); tristeza (caused by citrus tristeza virus); psorosis A and concave gum (caused by graft-transmissible agents); stubborn (caused by Spiroplasma citri); Phytophthora foot rot; and citrus slump (caused by Pratylenchus coffeae). Filamentous plugs observed in trees with citrus blight were also present in the xylem vessels of trees affected with stubborn, citrus slump, tristeza, and foot rot as well as in many healthy trees. Amorphous plugs were more numerous in trees with blight than in healthy trees. A similar type of plug was observed by light microscopy in trees with psorosis and concave gum. However, these amorphous-like plugs in trees with psorosis and concave gum could be differentiated from those present in trees with citrus blight by scanning and transmission electron microscopy. Thus, amorphous plugs are characteristic of blight trees and can be used for diagnosis along with zinc accumulation and reduced water uptake if care is taken to separate them from the amorphous-like occlusions that form in plants affected by other diseases.