Considering the frequent natural occurrence of mixed infection of two or more viruses in the same plant, the present research was developed with the objective of studying the symptomatological effects of mixed virus infections in melon (Cucumis melo), watermelon (Citrullus lanatus) and zucchini (Cucurbita pepo). The following virus species from the family Potyviridae genus Potyvirus were used in the study: Papaya ringspot virus (PRSV), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV). The symptomatological effects were evaluated in double and single infections in three melon hybrids Hy Mark, Gold Mine and Orange Flesh, two watermelon varieties Crimson Sweet and Charleston Gray and zucchini 'Caserta'. In greenhouse experiments, PRSV, WMV and ZYMV alone and in all possible double combinations were inoculated in ten-day-old melon, watermelon and zucchini plants, using ten plants of each hybrid or variety per virus combination. Inoculations were performed using leaf extracts from plants infected with each virus. Leaf samples from each virus combination were tested by ELISA against antisera specific for the respective viruses. The symptomatological effects in double virus infections revealed the existence of synergistic interactions between PRSV, WMV and ZYMV in melon, watermelon and zucchini. The double infections involving ZYMV showed severe symptoms and symptoms not present in ZYMV single infection.
