Measuring disease resistance accurately and reproducibly is a key requirement for the introgression of partial resistance genes into breeding lines. Here, a qPCR protocol is used to measure fungal biomass, using the wheat-Stagonospora nodorum pathosystem as a model. Seven cultivars of differing reported resistance levels were used. Fungal biomass taken at 220°C thermal days after inoculation accurately predicts the final grain weight loss. It is concluded that a test based on qPCR methods is specific, quantitative, rapid and objective. Such tests could provide useful and economic tools in the development of robustly resistant crop cultivars.