Involvement of RNA2 for systemic infection of Cucumber mosaic virus isolated from lily on zucchini squash.

A lily strain of Cucumber mosaic virus (LK-CMV) was not able to systemically infect zucchini squash (Cucurbita pepo), while Fny strain of CMV (Fny-CMV) caused systemic mosaic and stunting symptom at 4 days post-inoculation on the same host species. The pathogenicity of LK-CMV in zucchini squash was investigated by reassortments of genomic RNAs of LK-CMV and Fny-CMV for infection, as well as by pseudorecombinants generated from biologically active transcripts of cDNA clones of LK-CMV and Fny-CMV, respectively. The assessments of pathogenicity for LK-CMV indicated that RNA2 of LK-CMV was responsible for systemic infection in zucchini squash. In the protoplast of zucchini squash, the RNA accumulations of all constructed pseudorecombinants were indistinguishable and LK-CMV replication was slightly lower than that of Fny-CMV, suggesting that the inability of LK-CMV to infect squash plants was responsible for the poor efficiency of virus movement, rather than the reduction of replication function.