Ultrastructural effects of infection caused byTobacco rattle virustransmitted byTrichodorus primitivusin potato and tobacco tissues

Tobacco rattle virus (TRV), genus Tobravirus, is able to infect a broad range of plant species, possesses worldwide distribution and naturally infects a very large number of cultivated as well as ornamental plants. Members of the plant ectoparasitic nematode genera Trichodorus and Paratrichodorus transmit TRV in a semi-persistent way in a non-replicative process, where virus particles are transferred to the host plant through vector feeding on root epidermal and root hair cells. Our investigations concentrated on ultrastructural and anatomical effects of TRV strain PSG infection in situ following introduction into potato and tobacco tissues by Trichodorus primitivus. Our anatomical observations indicated necrotic changes of rhizodermis and cell wall deformations in primary cortex parenchyma and external phloem layers as a consequence of the interactions between Trichodorus–TRV–host plants. Ultrastructural analyses revealed TRV particles in rhizodermis, cortex and vascular roots of potato and tobacco tissues. These results indicate that TRV strain PSG was transferred into roots and also transported from cell to cell in all root tissues. Complete TRV PSG particles of two lengths were documented in companion cells, phloem fibre and parenchyma, as well as for the first time in immature and mature xylem tracheary elements and xylem parenchyma. Our findings suggested that TRV was systemically transported from the place of direct transfer by the vector to above-ground plant organs (especially leaves). The presence of TRV PSG particles in mesophyll and vascular leaf tissues confirmed our thesis. Moreover, we concluded that TRV systemic movement occurred not only in the phloem, but especially in the xylem, because virus particles were more frequently observed in xylem parenchyma and xylem tracheary elements.