RNA 2 of cucumber mosaic virus subgroup I strain NT-CMV is involved in theinduction of severe symptoms in tomato

A selection of cucumber mosaic virus (CMV) subgroup I strains originating f rom Asia and Fny-CMV isolated in USA were studied for their interaction wit h tomato plants. All strains caused mosaic, fernleaf expression and stuntin g of tomato plants. Symptom expression was relatively mild after infection with Fny-CMV, T-CMV, Le-CMV and MB-CMV, whereas strains PRC-CMV, NT-CMV and K-CMV caused more severe symptoms. Biologically active clones of NT-CMV RN As 2 and 3 were generated to construct pseudorecombinant viruses with Fny-C MV to map the symptom determining RNA. The pseudorecombinant FNF-CMV (RNAs 1 and 3 from Fny-CMV, RNA 2 from NT-CMV) showed a similar phenotype on toma toes to those caused by NT-CMV, whereas FFN-CMV (RNAs 1 and 2 from Fny-CMV, RNA 3 from NT-CMV) induced symptoms comparable to Fny-CMV. The data indica te that CMV RNA 2 of NT-CMV is involved in the induction of severe symptoms in tomato plants.