Influence of the Host Cultivar on Disease and Viral Accumulation Dynamics in Tomato under Mixed Infection with Potato virus X and Tomato mosaic virus

Abstract

The primary leaves of seedlings of tomato (Lycopersicon esculentum Mill.) cultivar Fukuju No. 2 (a common
Japanese cultivar that is susceptible to Tobacco mosaic virus (TMV, genus Tobamovirus) were inoculated at the
five-true leaf stage with the O strain of Potato virus X (PVX, genus Potexvirus) and with a mixture of that strain plus
Tomato mosaic virus (ToMV, genus Tobamovirus). Inoculation resulted in varying degrees of disease manifestation.
During the acute stage of the resulting severe disease (between 5 and 12 days postinoculation), PVX and ToMV levels
rose considerably in both the inoculated and the systematically infected leaves. Furthermore, levels of PVX in the
systemically infected upper leaves (positions 5 to 7) of plants with a mixed infection were three to six times as high as
in plants given the single infection, as determined by direct double antibody sandwich-enzyme linked immunosorbent
assay (DAS-ELISA). In tomato cv. GCR 236 (+/+), symptom manifestation and the accumulation of both PVX and
ToMV closely followed the pattern recorded for cv. Fukuju No. 2. In cv. GCR 237 (Tm-1) plants, however, only PVX
accumulated while ToMV whether inoculated singly or mixed with PVX was detected neither in the inoculated nor in
the systemically infected leaves even 14 days after inoculation. In contrast to other cultivars, SDS-PAGE, Western
blot and Northern blot hybridization did not reveal any enhancement of the coat protein and genomic RNA of PVX in
such systemically infected leaves. Consequently, the characteristic severe symptoms normally associated with mixed
infection in TMV-susceptible cultivars were absent.