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Studies on the Reason for Differential Transmissibility of Cauliflower Mosaic Virus Isolates by Aphids. M. C. Y. Lung, Department of Plant Pathology, University of Kentucky, Lexington 40506, Present address of senior author: Department of Plant Pathology, University of California, Berkeley 94720; T. P. Pirone, Department of Plant Pathology, University of Kentucky, Lexington 40506. Phytopathology 63:910-914. Accepted for publication 25 January 1973. DOI: 10.1094/Phyto-63-910.

Lack of aphid transmissibility of certain isolates of cauliflower mosaic virus (CIMV) could not be attributed to low virus concentration in entire leaves or in epidermal cells. A nontransmissible isolate had the same distribution and location in plant cells (determined by electron microscopy) as did transmissible isolates, and did not differ from the transmissible isolates in the number and distribution of inclusion bodies (determined by light microscopy). Virus particles of a nontransmissible isolate migrated at a rate intermediate to that of two transmissible isolates in agarose-acrylamide gel electrophoresis. The normally nontransmissible isolates could be transmitted by aphids from plants which were also infected with a transmissible isolate, or by aphids which had previously probed plants infected with a transmissible isolate. The results suggest that a factor necessary for aphid transmission of CIMV is present in leaves of plants infected with transmissible isolates that is not present in leaves infected with nontransmissible isolates. This factor may be acquired by aphids which probe leaves infected with transmissible isolates, subsequently enabling them to transmit the normally nontransmissible isolates.