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.

The phytochrome gene family, which is in Arabidopsis thaliana, consists of phytochromes A-E (phyA to phyE), regulates plant responses to ambient light environments. PhyA and phyB have been characterized in detail, but studies on phyC to phyE have reported discrepant functions. In this study, we show that phyD regulates the Arabidopsis gravitropic response by inhibiting negative gravitropism of hypocotyls under red light condition. PhyD had only a limited effect on the gravitropic response of roots in red light condition. PhyD also enhanced phyB-regulated gravitropic responses in hypocotyls. Moreover, the regulation of hypocotyl gravitropic responses by phyD was dependent upon the red light fluence rate.

Cotton (Gossypium spp.) is a major industrial crop supplying raw materials for the global textile, chemical, and pharmaceutical sectors. Phytochromes (PHYs) are key photoreceptors regulating plant growth and environmental adaptation, yet their functions in the complex allotetraploid genome of upland cotton (G. hirsutum) remain poorly understood. Here, we identified 29 PHY genes across four Gossypium species and performed comprehensive genomic and evolutionary analyses. We focused on GhPHYB1, a AD1-Dt PHYB homolog exhibiting light-inducible and stem-predominant expression. Virus-induced gene silencing (VIGS) revealed that GhPHYB1 negatively regulates vegetative elongation by modulating the GhHY5.A signaling axis. Additionally, GhPHYB1-silenced plants showed enhanced drought sensitivity, with reduced proline content, elevated malondialdehyde (MDA) and H₂O₂ levels, and impaired photosynthesis efficiency (Fv/Fm). Heterologous expression in yeast further confirmed its role in enhancing osmotic stress tolerance. Collectively, these findings establish GhPHYB1 as a dual regulator of plant architecture and drought tolerance, offering a promising target for molecular breeding tolerancetoleranceof industrial cotton varieties.

Cotton (Gossypium spp.) is a major industrial crop supplying raw materials for the global textile, chemical, and pharmaceutical sectors. Phytochromes (PHYs) are key photoreceptors regulating plant growth and environmental adaptation, yet their functions in the complex allotetraploid genome of upland cotton (G. hirsutum) remain poorly understood. Here, we identified 29 PHY genes across four Gossypium species and performed comprehensive genomic and evolutionary analyses. We focused on GhPHYB1, a AD₁-Dt PHYB homolog exhibiting light-inducible and stem-predominant expression. Virus-induced gene silencing (VIGS) revealed that GhPHYB1 negatively regulates vegetative elongation by modulating the GhPIF4 signaling axis. Additionally, GhPHYB1-silenced plants showed enhanced drought sensitivity, with reduced proline content, elevated malondialdehyde (MDA) and H₂O₂ levels, and impaired photosynthesis efficiency (F_v/F_m). Heterologous expression in yeast further confirmed its role in enhancing osmotic stress tolerance. Collectively, these findings establish GhPHYB1 as a dual regulator of plant architecture and drought tolerance, offering a promising target for molecular breeding of industrial cotton varieties.