A miniaturized Arabidopsis thaliana - Botrytis cinerea seedling pathosystem and the GreenDayz workflow for longitudinal image-based phenotyping

Plant-pathogen interactions are strongly influenced by host developmental stage, yet many Arabidopsis thaliana-Botrytis cinerea assays remain centred on mature rosette leaves and rely on inoculum loads that may exceed those involved in a primary infection. We established a miniaturized in vitro A. thaliana-B. cinerea seedling pathosystem initiated with a very low conidial dose (nominally ~25 conidia per plate) compatible with both destructive molecular sampling and repeated, non-destructive RGB imaging. The pathosystem was coupled to a low-cost smartphone photo station and to GreenDayZ Phenotyping, a guided image-analysis application with an intuitive graphical interface that standardizes longitudinal RGB image processing and extracts quantitative colour-based phenotypes. Together, the pathosystem and GreenDayZ Phenotyping provide an accessible and reproducible framework for longitudinal phenotyping of low-inoculum seedling infections, in which image-derived trajectories can be aligned with independent molecular readouts.