Antagonism of Cucumber green mottle mosaic virus against Tomato leaf curl New Delhi virus in zucchini and cucumber

Tomato leaf curl New Delhi begomovirus (ToLCNDV) (genus Begomovirus, family Begomoviridae) and Cucumber green mottle mosaic tobamovirus (CGMMV) (genus Tobamovirus, family Virgaviridae) cause diseases in cucurbit crops and are of increasing importance in many parts of the world. Both virus species belong to different families and have different modes of transmission, but share common hosts. We examined single and mixed infections of these viruses in cucumber and zucchini. Cucumber plants single-infected with CGMMV and co-infected with ToLCNDV, produced identical tobamovirus-specific symptoms, and had reduced growth and number of fruits when compared with single ToLCNDV infections. Zucchini infected with CGMMV remained symptomless but when infected with ToLCNDV only, most developed severe begomovirus-specific symptoms, and had reduced vegetative development and less fruits. Fewer zucchini plants with ToLCNDV co-infected with CGMMV produced symptoms than those infected with ToLCNDV only. When inoculated with CGMMV, this tobamovirus accumulated at similar rates in single and mixed infections with ToLCNDV in cucumber as well as zucchini, whereas the begomovirus accumulated significantly less when co-infected with CGMMV. The results suggest the existence of an antagonistic effect of CGMMV against ToLCNDV accumulation in cucumber. Such effect would also explain similar differences in viral loads, the vegetative and reproductive development, and the reduced symptom expression in zucchini.