Survey of vegetable crops in different regions Ismailia Governorate in Egypt conducted detection of Watermelon mosaic virus. The virus detected using DAS-ELISA form naturally infected watermelon and squash plants, exhibiting severe yellow mosaic, vein clearing, blistering and distortion of leaves. Isolation and identification of WMV was carried out by studying host range, symptomatology, modes of transmission, serological reaction and electron microscopic examination. The molecular detection of WMV done using RT-PCR with specific primers designed for coat protein gene. RT-PCR products 825bp of coat protein gene of WMV cloned and then sequenced. The coat protein gene of the Egyptian isolate of WMV showed nucleotide sequences similarity ranged from 95%-99% with different isolates available in Gene Bank. The experiments carried out under greenhouse condition, (HRI) - (VRD) from2014 to 2017. Five squash inbred lines used making half diallel to produce 10 hybrids to determine performance some variables under WMV infection condition. A complete block design was used. The evaluation process performed through two experiments. First experience, cultivation the genotypes with a commercial hybrid after infection to evaluate the performance of genotypes for yield and some characteristics. Therefore the percentage of reduction in yield estimated.  The second experiment without infection and evaluate the performance for the same variable. The study found that, there were significant differences between all the genotypes that were inoculated and noninoculated. The reducing in yield ranged 14.6: 30%.  Therefore, the study recommended attention to the hybrid that achieved a decrease of 14.6% by continuing to work on it.