WSPSorter: a real-time integrated system for non-destructive purity sorting of watermelon seeds based on rotary singulation and near infrared spectroscopy.

BACKGROUND

Watermelon seed purity is a critical determinant of varietal authenticity and production quality. In hybrid seed production, however, distinguishing between maternal seeds and hybrid seeds at the single-seed level remains challenging because their phenotypic differences are subtle. Conventional purity identification methods are often destructive, labor-intensive, and time-consuming and are poorly suited to the practical demand for rapid, continuous, single-seed online sorting.

METHODS

To address these challenges, this study developed the Watermelon Seed Purity Sorter (WSPSorter), an integrated real-time sorting system based on rotary singulation, near-infrared (NIR) spectroscopy, and pneumatic actuation. The system achieves stable single-seed delivery through a rotary seed-metering mechanism, acquires single-seed spectral information in real time, and combines NIR spectroscopy with an Extreme Gradient Boosting (XGBoost) classification model to discriminate maternal seeds from hybrid seeds.

RESULTS

The optimal model, combining wavelet denoising, the successive projections algorithm (SPA), and XGBoost, achieved accuracies of 98.89% on the validation set and 97.78% on the independent test set. WSPSorter achieved an average inter-sample interval of 254.88 ms, corresponding to a practical throughput of approximately 4.0 seeds per second. Sorting performance, evaluated against PCR-derived reference labels, reached 94.04% for maternal seeds and 90.05% for hybrid seeds.

DISCUSSION: These results indicate that WSPSorter effectively connects single-seed spectral sensing with real-time physical sorting, providing a feasible engineering solution for rapid, non-destructive, and automated purity sorting of watermelon seeds.