Three viruses transmitted by aphids (non-persistent transmission) are responsible of strong yield losses on squash crops in France and around the world: Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV). For each virus, different biological, serological and molecular groups were described. The resistance is polygenic for CMV, ZYMV and with a major gene for WMV but always with an intermediate resistance. The evaluation of squash resistance to viruses and the assessment of symptoms are complex due to the partial and not complete resistance and the quantitative results observed. It is important to describe the different levels of virulence of virus strains and to identify the different levels of resistance of squash varieties. There are currently no harmonized protocols to define the levels of partial resistance of squash to these viruses. The aim of this project, in collaboration between GEVES, INRAE and breeding companies (HMClause, Gautier, Monsanto, Rijk Zwaan, Sakata, Syngenta) was to acquire a better knowledge of levels of squash resistance and to define robust resistance tests to these viruses. Based on the INRAE’s characterized collection of strains of viruses, three strains per virus (with different virulences and from different groups) were selected. These strains and different protocols from INRAE and partners (stage of inoculation, optimal conditions of test, notation scale) were compared, on a panel of commercial varieties with different levels of resistance, to define for each virus a robust resistance test. One strain per virus, making it possible to differentiate the different levels of resistance of varieties, was selected. For each virus, a resistance test and reference materials (strain and controls) were validated. The reference collection of GEVES was characterized for the three viruses. These new protocols, used for CTPS registration, will be proposed to CPVO and UPOV for a harmonized use.