Evaluation of Quality Traits in Relation to Mechanical Harvesting for Screening Excellent Materials in Gossypium barbadense L. Germplasm Resources

Sea Island cotton is renowned for its superior fiber quality. Although mechanical harvesting has the potential to significantly increase efficiency and reduce the production cost of Sea Island cotton, there is still little research in this area. In this study, we analyzed 240 Sea Island cotton germplasm resources and evaluated 19 traits related to mechanical harvesting. The coefficient of variation ranged from 5.42% to 66.96%, and the genetic diversity index spanned from 1.57 to 2.07. In most traits studied, there was a strong correlation between the height of the first fruiting branch and the defoliation rate. The 19 traits were categorized into 6 factorial groups by principal component analysis, in which the defoliation factor contributed the most (30.89%). The cluster analysis divided the 240 cotton accessions into four main groups, with the second group exhibiting favorable mechanical harvesting characteristics such as higher defoliation rate and first fruit branch height. Using stepwise regression, a model was constructed with the joint evaluation score F-value as the response variable and eight traits (X1: PH, X2: SNB, X3: SBN, X4: MBL, X5: AFBM, X7: MLIA, X8: NB, and X13: 15 d DR) as predictors: Y = −7.2 + 0.01X1 + 0.23X2 + 0.192X3 + 0.038X4 + 0.007X5 + 0.014X7 + 0.025X8 + 2.952X13. Selected materials suitable for machine harvesting, such as MoShi729, were identified. This study provides valuable theoretical insights into the mechanical harvesting of Sea Island cotton germplasm resources and identifies promising materials for targeted breeding and improvement programs.