VIEW ARTICLE

Cytology and Histology

Comparison of Water Flow and Xylem Plugging in Declining and in Apparently Healthy Citrus Trees in Florida and Argentina. L. W. Timmer, Professor, University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred 33850; R. H. Brlansky(2), J. H. Graham(3), H. A. Sandler(4), and J. P. Agostini(5). (2)(3)(4)Associate professor, assistant professor, and assistant in plant pathology, respectively, University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred 33850; (5)Ingeniero Agronomo, Instituto Nacional de Tecnologia Agropecuaria, Montecarlo, Misiones, Argentina. Phytopathology 76:707-711. Accepted for publication 6 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-707.

Citrus blight (CB) in Florida and citrus declinamiento (CD) in Argentina are declines of unknown etiology brought about by xylem dysfunction. Water flow and plugging were determined to a depth of 4 cm from the cambium in cores taken from trunks of trees. In healthy trees, water flow was high and amorphous plugs were rare in all segments. In CB- and CD-affected trees, there was little or no water flow in the core segments deeper than 1 cm from the cambium, and amorphous plugs were numerous. In Argentina, apparently healthy but low-vigor (LV) trees on rough lemon, Rangpur lime, Cleopatra mandarin, and sweet orange rootstocks took up little water by the syringe injection method, water conductivity was normal only in the segment 0-1 cm from the cambium, and amorphous plugs were common. When examined by scanning electron microscopy, plugs in LV trees were typical of those in CB and CD trees. Thus, even these LV trees in Argentina may be affected by the disease. Affected trees in Argentina on the highly susceptible trifoliate orange rootstock decline, but those on less susceptible rootstocks apparently produce enough unplugged vessels each year in this humid, subtropical area to avoid sufficient plugging of the xylem to cause canopy decline. There was an inverse relationship between rootstock susceptibility and water flow through the outer 2 cm of trunk wood in Argentina.