Mechanism and Prediction of Gray Jujube Fruit Quality Using Explainable ANN.

Abstract

Gray jujube ( Ziziphus jujuba Mill) is an important economic fruit crop in Xinjiang, China, whose fruit quality is regulated by complex interactions among tree architecture, physiological functions, and environmental factors. Based on 2 years of field experiments, we developed an interpretable artificial neural network model integrating 13 structural and physiological indicators to predict four quality parameters: vitamin C (VC), soluble sugar, titratable acid, and sugar-acid ratio. The model architecture was optimized through Bayesian optimization, resulting in a 13-4-1/13-5-1 network structure with high prediction accuracy ( R 2 = 0.89-0.98). Biological interpretation of the connection weights revealed that the elongation of bearing shoots (1.2-3.1 cm/month) and SPAD values (33-41.5) were key drivers of VC accumulation, reflecting their roles in photosynthate transport and light-harvesting efficiency. Canopy structural characteristics, particularly leaf inclination angles of 26°-34° combined with a direct beam transmittance of 0.32-0.43, were found to synergistically enhance sugar accumulation by optimizing light distribution while maintaining sufficient gas exchange. Furthermore, net photosynthetic rates exceeding 12 μmol·m -2 ·s -1 significantly reduced organic acid content, indicating a shift in carbon partitioning toward sugar synthesis. These findings demonstrate that the model successfully bridges computational analysis with biological processes, providing both a predictive tool and mechanistic insights for gray jujube quality management. The integration of architectural, physiological, and environmental parameters in this framework offers a comprehensive approach for precision cultivation of this important crop.

Code and data availability

The paper's phenotyping measurements (13 tree structure/physiological indicators and four fruit quality traits) and ANN/SHAP analysis are not publicly available: the Data Availability Statement states data access is temporarily restricted and obtainable only by applying to the corresponding author. No public code, data

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