Nontransmission of Citrus Blight by Soil. L. W. Timmer, University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred 33850. J. H. Graham, University of Florida, IFAS, Citrus Research and Education Center, Lake Alfred 33850. Plant Dis. 76:323. Accepted for publication 3 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0323D.
Mature Valencia sweet orange (Citrus sinensis (L.) Osbeck) trees
on rough lemon rootstock (C. jambhiri Lush.) were inoculated with
soil from beneath blight-affected trees of the same combination in
April 1985. About 0.5 m3 of soil and roots from beneath each tree
was removed with a VerMeer tree spade and replaced with the same
volume of soil from beneath a blighted tree. Soil beneath control
trees was removed and replaced with soil from other control trees.
Ten single-tree replications were arranged in a randomized block
design, with one guard tree between test trees. Donor trees had typical
blight symptoms, water uptake of 0.0 mil sec by the syringe injection
test (1), and 11.8 ppm of zinc in the trunk wood. By 1990, no symptoms
of citrus blight had appeared in any tree. Average annual water uptake
was 0.52 mil sec in treated trees and 0.64 mil sec in controls and was
not significantly different in any year. Zinc concentrations averaged
2.90 µg/g in treated trees and 2.96 µg/g in control trees and were
not significantly different. Although blight has been transmitted root-to-root and by root-piece grafts, it was not spread after 5 yr by soil
and roots in the absence of a graft union.