Comparison of Citrus Tree Declines with Necrosis of Major Roots and Their Association with Fusarium solani. J. H. Graham, University of Florida, Institute of Food and Agricultural Sciences (IFAS), Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. R. H. Brlansky, L. W. Timmer, and R. F. Lee, University of Florida, Institute of Food and Agricultural Sciences (IFAS), Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850; L. J. Marais, Outspan Citrus Centre, Nelspruit, South Africa; and G. S. Bender, Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 69:1055-1058. Accepted for publication 1 July 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1055.

Necrosis of major roots (> 1 cm in diameter) of Dancy tangerine on rough lemon rootstock affected by tangerine collapse (TC) in Florida resembled that on tangerine trees with citrus blight (CB) in Florida and that on navel orange on trifoliate orange rootstock with dry root rot (DRR) in California and that on Eureka lemon on rough lemon rootstock in South Africa. The initial symptom of TC was leaf wilt on trees bearing large crops of fruit; root necrosis was present only on trees that were at least mildly declined and had reduced starch in wood. Fusarium solani was isolated from necrotic wood of roots of trees affected with each of these declines. Reduced water uptake and zinc accumulation in trunkwood occurred in trees affected by CB but not in trees affected by DRR and TC. Golden plugs in the xylem of trees affected by DRR and TC resembled those of CB when observed by light microscopy but were filamentous compared with the solid, amorphous plugs of CB when observed by scanning electron microscopy. Inoculation of trifoliate orange seedlings with F. solani only caused root necrosis when starch reserves in the wood were first reduced by decapitation and root girdling. Fusarium appears to be a primary colonizer of citrus roots after starch reserves are depleted.