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Detection of a Latent Infectious Agent That Protects Against Infection by Chrysanthemum Chlorotic Mottle Viroid. R. K. Horst, Department of Plant Pathology, Cornell University, Ithaca, New York 14853; Phytopathology 65:1000-1003. Accepted for publication 3 April 1975. DOI: 10.1094/Phyto-65-1000.

A latent infectious agent (ChCMV-NS) that protects against chrysanthemum chlorotic mottle viroid (ChCMV) was found in cultivars of Chrysanthemum morifolium; it produced no recognizable symptoms, but is detectible by its complete protection against the severe strain of chrysanthemum chlorotic mottle viroid. At least 8 days of incubation are required after inoculation of ChCMV-NS for complete protection against ChCMV. Optimum detection of ChCMV-NS occurred at 21 C and the optimum for detection of ChCMV from crude extracts of source plants was 21 to 24 C. Detectible infectivity of ChCMV was increased with illumination intensities up to 30,128 lx. The existence of a latent infectious agent is important in indexing programs, since current indexing procedures will not detect the latent agent.