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Infectivity Studies of Avocado Sunblotch Disease Causal Agent, Possibly a Viroid Rather than a Virus. P. R. Desjardins, Professor, Department of Plant Pathology, University of California, Riverside 92521. R. J. Drake, Staff Research Associate, and S. A. Swiecki, Laboratory Assistant, Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 64:313-315. Accepted for publication 1 November 1979. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-313.

The causal agent of avocado sunblotch disease was mechanically transmitted from avocado to avocado by the razor-slash technique. Infectious material in various extracts from diseased fruit tissue also was transmitted to avocado by this method. The lack of typical virions in diseased tissues and in tissue extracts, the lack of association of microorganisms, and the pronounced thermal stability of the infectious agent suggested a nature other than viral. In extraction procedures not involving phenol, the infectious agent was in higher concentration in high-speed supernatants than in high-speed pellets, suggesting a low molecular weight substance. Also, the agent in such extracts appeared to have some sensitivity to RNase. Apparently, the causal agent has many properties characteristic of viroids that are not characteristic of viruses.