BIR and LCD: conceived of and designed the experiments, provided populations and resources and reviewed the manuscript. JL: conducted process and statistical analysis of RNA-Seq data. RSL: provided first field assessment of symptoms and designed the evaluation scale, MO: performed statistical analysis of RNA-Seq. PB: conceived of and designed the experiments, collected phenotypic data, performed molecular biology and microbiology laboratory work, genetic analysis and statistical analysis, and wrote the paper. KB and RT: conceived and designed greenhouse inoculation assays, collected phenotypic data, performed statistical analyses and contributed to and reviewed the manuscript. WFW: performed field identification and isolation of D. ampelina and reviewed the manuscript.