Localization of Zucchini yellow mosaic virus to the veinal regions and role of viral coat protein in veinal chlorosis conditioned by the zym potyvirus resistance locus in cucumber

The zym locus in cucumber (Cucumis sativus L.) is marked by multiple alleles conferring resistance to the potyvirus, Zucchini yellow mosaic virus (ZYMV), Cotyledon inoculation of greenhouse grown plants expressing the zym(Dina) allele results in a distinct pattern of veinal chlorosis limited to a single systemic leaf, leaf-inoculated plants remain free of symptoms. Inoculation of cotyledons of plants of different growth stages indicated that the virus moved to the leaf that was newly emerging at the time of cotyledon infection where it Own remained localized to the veinal regions for up to 30 days post-inoculation (d.p.i). Cotyledon removal experiments indicated that tire inability of ZYMV to spread within the uninoculated leaf, or to infect inoculated leaves, was riot due to the inability to replicate in leaves. Chimeric viruses generated from a strain of ZYMV that did not induce the veinal chlorosis response, indicated that the coat protein amino terminus, which has been shown to be involved in long distance movement, affected occurrence of veinal chlorosis. In the growth chamber, inoculation of the first leaf, but not subsequent leaves, gave a high percentage of plants expressing veinal chlorosis. Together, these observations suggest that resistance conferred by zym(Din)a is developmentally regulated and occurs at the level of systemic movement. (C) 2002 Elsevier Science Ltd.