The disease virus yellows of sugar beet is caused by infection with different viruses. In this project, we aim to identify the viruses causing the disease as well as mechanisms and plant genes giving resistance or tolerance to virus infection. This would allow improved management strategies, including breeding of virus-resistant crop cultivars. Viruses and associated RNA satellites are being identified through RNAseq of RNA isolated from field samples of sugar beet and oilseed rape. Differentially expressed genes in response to virus infection are identified by RNAseq for one susceptible and one tolerant genotype of sugar beet. In addition, genes for virus tolerance are mapped in sugar beet by QTLseq and genome sequencing.