REASSESSING THE LINK BETWEEN SOLUBLE SOLIDS AND SUGARS IN MELON: FTIR MODELS AS AN ALTERNATIVE TOOL

REASSESSING THE LINK BETWEEN SOLUBLE SOLIDS AND SUGARS IN MELON: FTIR MODELS AS AN ALTERNATIVE TOOL Salvador Rosellóa, Ana Pérez de Castrob, Belén Picóc, María García-Cabrerac, Jaime Cebolla-Cornejob* aJoint Research Unit UJI/UPV - Improvement of Agri-Food Quality, Department de Ciències Agràries i del Medi Natural, Universitat Jaume I, Avda. Sos Baynat s/n, 12071, Castellón, Spain bJoint Research Unit UJI/UPV - Improvement of Agri-Food Quality, COMAV, Universitat Politècnica de València, Cno. de Vera, s.n, 46022, València, Spain cCOMAV, Instituto de Conservación y Mejora de la Agrodiversidad, Universitat Politècnica de València, Cno. de Vera, s.n, 46022, València, Spain *Corresponding author: [e-mail] ABSTRACT Soluble solids content (SSC), expressed in °Brix, has traditionally been used as a proxy for sugar content in melon breeding and quality control. However, in a diverse set of Ibericus melons, only moderate correlations (R² ≈ 0.60) were found between SSC and total sugars or sucrose, and no correlation was observed with hexose content or the hexose-to-sucrose ratio. Moreover, the sensitivity of SSC under high selection pressure remained below 50–60%. In contrast, FTIR models calibrated for specific trials predicted sucrose, glucose, fructose, citric acid, total sugars, sucrose equivalents, and the hexose-to-sucrose ratio with mean R²p values of 0.73–0.88 and %RMSEP values of 3.5–8.9%, outperforming previous NIR and FTIR models. General models, though trained on larger datasets, performed similarly to the weakest specific models. Trial-specific models validated on external datasets achieved R²p values of 0.79–0.94 (mean 0.84) and %RMSEP values of 3.6–28.7% (mean 11%), without requiring recalibration. FTIR thus offers a robust alternative to SSC for high-throughput phenotyping. Keywords: soluble solids content, brix, breeding, FT-MIR, spectroscopy, selection, Cucumis melo L. FUNDING SOURCES Funding was partially provided by MCIN/AEI/10.13039/501100011033/ and by "ERDF: A way of making Europe" grants AGL2014-53398-C2-2-R, AGL2017-85563-C2-1-R-AR, PID2020-116055RB-C21 and PID2023-151202OB-C21, and by grant PROMETEO/2021/072 (to promote excellence groups) funded by Conselleria de Educación, Universidades y Empleo (Generalitat Valenciana, Spain).