Quantifying naturally colored cotton fiber color intensity using RGB image-based phenotyping

Abstract

Abstract Image-based phenotyping has become an innovative approach in plant breeding. This study quantified fiber color intensity in Gossypium hirsutum L. genotypes and evaluated the effect of boll position in the upper, middle, and lower plant canopy thirds. Five cultivars and twelve F 2:3 lines were assessed by sampling five plants per plot, collecting three bolls per third, and photographing them with a standard color card. Images were processed using ImageJ and analyzed in R with the FIELDimageR package to calculate the Brightness Index (BI), Saturation Index (SI), and Normalized Green-Red Difference Index (NGRDI). Color card calibration increased mean values without changing genotype groupings. The upper third showed 6.25% lower color intensity, with no significant genotype × third interaction. SI efficiently discriminated genotypes, while BI strongly correlated with fiber Uniformity Index, Strength, and Upper Half Mean Length (R² = 0.77, 0.80, and 0.88, respectively), supporting its use in breeding programs.