Non-Invasive Detection of Water Stress in Jalapeño Pepper (Capsicum annuum L. var. Huichol) Through Foliar Vascular Network Analysis Using Multi-Modal VIS-NIR and Thermal Imaging

Water stress is a critical limiting factor in horticultural crop productivity. This study presents a non-invasive approach for detecting water stress in jalapeño pepper (Capsicum annuum L. var. Huichol) through visible–near-infrared (VIS-NIR) imaging-based quantification of the foliar vascular network under controlled conditions. Nine plants were subjected to three irrigation regimes (100%, 50%, and 0% of daily water loss) and monitored over 13 days, acquiring VIS-NIR and LWIR images under light and darkness conditions. Using a digital image processing pipeline, foliar vascular networks were segmented from VIS-NIR images, and the vascular proportion index (Rv) was computed. A factorial ANOVA revealed significant main effects for irrigation treatment (F = 11.01, p < 0.001), illumination (F = 13.01, p < 0.001), and spectral modality (F = 422.77, p < 0.001), with the spectral band accounting for the highest variance (ηp2 = 0.079). The VIS-NIR + Light configuration produced the clearest treatment discrimination, with significant pairwise differences between 50% WL and both 100% WL (MD = 0.025, p < 0.0001) and 0% WL (MD = 0.020, p = 0.0001). This VIS-NIR-based technique offers a practical, scalable alternative for real-time monitoring of plant water status in horticultural systems.