Pathway for Phloem-Dependent Movement of Pepper Mottle Potyvirus in the Stem of Capsicum annuum

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Abstract
Phloem-dependent movement of pepper mottle potyvirus (PepMoV) through Capsicum annuum occurs in a defined pattern through the stem and into uninoculated leaves. The route of movement of PepMoV through the stem of C. annuum ‘Early Calwonder’ was tracked using immunotissue blot analysis and immunomicroscopy. Virus was shown to move from the inoculated leaf down the stem toward the roots via the external phloem. At some location between the cotyledonary node and the roots, PepMoV entered the internal phloem through which it rapidly spread upward the length of the stem to the young tissues. Translocation of PepMoV through the stem occurred in an asymmetric fashion, i.e., virus remained on the side of the stem to which the inoculated leaf was attached as it translocated the length of the stem. Spread and accumulation of PepMoV into uninoculated leaves appeared to occur in a source-to-sink pattern similar to that described for the flow of photoassimilates and similar to other virus and viroid-host systems.