Digital techniques and trends for seed phenotyping using optical sensors

•Optical sensors are highly-promising for seed phenotype digitization.•Spectroscopy, digital imaging, and 3D reconstruction are primarily used digital techniques.•Optical sensors can detect both visible external and invisible internal phenotypes.•Matched optical sensors can effectively reduce resource loss in seed phenotype evaluation.•Future research should focus on phenotype equipment, platform, and data processing algorithms for automatic, integrated, and intelligent evaluation.