Rapid and non-destructive evaluation of seed quality of Chinese fir by near infrared spectroscopy and multivariate discriminant analysis

Chinese fir (Cunninghamia lanceolata (Lamb) Hook) is a promising timber species for planting in the sub-tropical ecosystem. However, the germination rate of Chinese fir seed lots is low, and viability determination by conventional methods (germination test and tetrazolium test) is time-consuming and destructive. Therefore, the aim of this study was to investigate the potential of Near Infrared (NIR) spectroscopy for rapidly and non-destructively determining viability of Chinese fir seeds. A total of 450 seeds was first identified as viable, empty, or dead (n = 150 seeds per seed lot fraction) by digital X-ray and their viability was further confirmed by germination test. NIR reflectance spectra were collected from single seeds using XDS Rapid Content Analyzer from 780 to 2500 nm. Classification models were developed on calibration set (n = 300 seeds) by Orthogonal Projection to Latent Structures-Discriminant Analysis (OPLS-DA) using the entire or selected NIR regions, and the fitted models were validated using external test set (n = 150 seeds). The model’s ability to recognize members (sensitivity) while rejecting non-members (specificity) of a given class was 100% for viable and dead seeds and 98% for empty seeds, attesting to the model’s robustness. When the model was fitted in the shorter NIR region (780–1100 nm), the sensitivity and specificity reached 100% for all seed lot fractions. The mean classification accuracy was 99% in the full and longer NIR regions and 100% in the shorter NIR region. The spectral differences among seed lot fractions could be attributed to differences in seed coat chemical composition in empty and dead seeds, presumably tannin content, and major storage reserves in viable seeds, notably fatty acids, proteins, and carbohydrate. It can be concluded that NIR spectroscopy has a great potential to evaluate Chinese fir seed quality, which could be applied in the development of an on-line sorting system.