Detection of Botrytis cinerea on strawberry leaves upon mycelial infection through imaging technique

•Mycelial age significantly affected the virulence of different Botrytis isolates.•Mycelial age should be considered when comparing the virulence of different Botrytis isolates by mycelium infection.•Fv/Fm followed by mAriIdx had strong correlations with disease severity caused by Botrytis mycelium inoculation.•Fv/Fm could be further developed for early detection of grey mold disease on strawberry production. Imaging techniques are increasingly used for the early detection of plant diseases. Botrytis cinerea is an economically damaging disease in strawberries. Although conidia are the primary inoculum for infection, secondary inoculum by mycelial fragments contributes also to disease spreading. Here mycelial inoculations were used on strawberry leaves to explore potential indicators for early detection of B. cinerea by using multispectral imaging. The pathogenicity of 15 Botrytis strains using mycelium plugs originating from 5-day-old and 13-day-old active growing cultures as inoculum was assessed. Overall, 5-day-old mycelium showed a higher virulence. Therefore 5-day-old mycelium was chosen as inoculum for image-based detection. Changes in the photosynthetic performance of strawberry leaves upon infection were recorded by Fv/Fm and changes in two vegetation indices. The chlorophyll index (ChlIdx) and the modified anthocyanin reflection index (mAriIdx) were monitored using a multispectral phenotyping platform. Fv/Fm followed by mAriIdx highly correlated with the disease index and both have the potential to be further developed for the early detection of grey mold on strawberry leaves.