VIEW ARTICLE

Physiology and Biochemistry

ELISA and Immunocytochemical Detection of Fusarium solani-Produced Naphthazarin Toxins in Citrus Trees in Florida. S. Nemec, U.S. Department of Agriculture, Agricultural Research Service, 2120 Camden Road, Orlando, FL 32803; S. Jabaji-Hare, and P. M. Charest. Département de Phytologie, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4. Phytopathology 81:1497-1503. Accepted for publication 19 June 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-1497.

Naphthazarin toxins of Fusarium solani were detected by competitive ELISA analysis in xylem fluid of roots rotted by F. solani and symptomless scaffold roots and branches of healthy-appearing and diseased citrus trees in ridge and flatwoods Florida groves. Studies concentrated on blight, a wilt disease with an undefined cause and etiology, to determine if F. solani is a causal factor of the disease. Healthy-appearing roots of trees with blight symptoms in six groves contained up to 11.4 times more toxin than roots of healthy trees in the same groves. In blight-diseased trees from these groves, median toxin values per root and the percentage of roots positive for toxin were higher than for healthy trees. Root-rotted roots from blight-diseased trees in two groves contained 112 and 3.4 times more toxin than healthy-appearing roots from the diseased trees. In two groves, one containing tristeza-diseased trees and the other foot rot-diseased trees, toxin concentrations were greater in diseased compared with healthy trees only in the foot rot site. Toxin concentrations were not different in healthy-appearing roots of healthy tangerine and sweet orange trees on Citrus limon ‘Milam’ in adjacent groves in a burrowing nematode site. Significantly more toxin was present in branches of blight than in healthy trees in two of three groves. In fibrous roots infected by F. solani, immunocytochemical localization of naphthazarins was present in fungal cell walls and associated electron-dense substances on the outer surface of the hyphae. In the fungal cytoplasm, the toxin was localized in nonmembrane-bound electron-lucent areas. The presence of naphthazarin toxins in blight-diseased trees as well as those with other diseases suggests the nonspecificity of F. solani pathogenic activity on various rootstocks. Therefore, in situ toxin concentrations high enough to trigger pathogenic effects in susceptible rootstocks may be required to cause blight.