Development of Tomato Fruit Stage Index (TFSI) to characterise different fruit growth stages of tomato using multivariate techniques

Tomato [ Solanum lycopersicum L.] fruits are frequently picked at various growth stages from mature green towards red ripe stages, mainly based on the widely used visual grading schemes. Which in many cases are inaccurate, time intensive and do not support high-tech agriculture, which needs accurate classification of tomato fruit development and ripening. The present study was conducted to identify the diverse developmental stages of tomato fruits using biophysical and biochemical parameters combined with multivariate techniques. Results showed that among the genotypes considered, the biophysical parameters like length, width, biomass and firmness was in the range of 23.65–62.28 mm, 24.99–80.47 mm, 2.11–4.85 g/fruit, 1.67–4.43 kg/cm 2 , respectively. The biochemical parameters like total soluble solids, titratable acidity, beta carotene, ascorbic acid and lycopene content was in the range of 3.99–6.5°Brix, 0.38–0.59%, 1.83–12.06 ppm, 83.12–339 mg/100 g and 4.11–76.77 mg/100 g, respectively. Multivariate techniques like principal component analysis (PCA), Hierarchical Cluster Analysis (HCA), and discriminant analysis (DA) were used to develop a new index called Tomato Fruit Stage Index (TFSI), which could group the tomato fruits from different growth developmental stages into categories like immature green, mature green and ripening stages. The range of TFSI was found to be 0 to 1. TFSI was < 0.3 for immature green, 0.3–0.42 for mature green and > 0.42 for red ripe fruit stages. The validation of TFSI showed that it was effective (R 2 = 0.985**) in identifying the fruit developmental stages and could be useful in future for routine categorisation and determination of the fruit developmental stages in tomato genotypes by the processing industries. Graphical abstract