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Partial Purification of Viruslike Particles Associated with the Citrus Tristeza Disease. M. Bar- Joseph, Virus Laboratory, The Volcani Institute of Agricultural Research, Bet Dagan, Israel; G. Loebenstein(2), and J. Cohen(3). (2)(3)Virus Laboratory, The Volcani Institute of Agricultural Research, Bet Dagan, Israel. Phytopathology 60:75-78. Accepted for publication 28 July 1969. DOI: 10.1094/Phyto-60-75.

Threadlike particles associated with the tristeza disease of citrus were partially purified, employing a combination of gentle grinding, precipitation by polyethylene glycol and differential centrifugation, and using electron microscopy as an assay. Particles in negatively stained dip preparations from leaves or stem bark exhibited a normal length of 200 mµ and a width of 10-11 mµ. Sedimentation constants of purified preparations, determined in sucrose density gradients, ranged from 105 to 131 S, with a calculated value of 140 S (±10) at zero depth. In purified preparations, normal length particles amounted to 26%, whereas variations in the procedure resulted in fragmentation of almost all particles. In different tissues of four citrus varieties, the highest concentrations of particles were always found in the stem bark. Bark from Key limes was the best source for extraction. In Key lime leaves, particle concentration was correlated with symptom intensity.