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Key message: Two regions located at chromosome A05 and D04 were found to be significantly associated with 0–0.5 mm and 0.5–2 mm diameter roots, respectively, and two candidate genes related to root development were identified. Roots absorb water and nutrients, and play an important role in plant growth. However, there are few genetic developmental studies on cotton root structural traits. In this study, we used 200 upland cotton (Gossypium hirsutum L.) varieties to analyze the phenotypic variation of 43 traits. A total of 2001 related single-nucleotide polymorphism (SNP) sites located within or near 1046 genes were detected through a genome-wide association study (GWAS). The 32 root traits were linked to SNPs that corresponded to 317 nonrepetitive genes. For SNPs associated with root length and 0–0.5 mm diameter root traits, a significant peak appeared on chromosome A05 (between 21.91 and 22.24 Mb). For SNPs associated with root surface area, root volume and 0.5–2 mm diameter root traits, a significant peak appeared on chromosome D04 (between 7.35 and 7.70 Mb). Within these two key regions, SNPs were detected in the promoter and coding regions of two candidate genes, GhTRL1-A05 and GhPIN8-D04. The expression levels of these two genes also changed significantly according to transcriptome sequencing and quantitative real-time PCR (qRT–PCR). After silencing the GhTRL1 and GhPIN8 genes via virus-induced gene silencing (VIGS), we found that the plants expressing TRV2::GhTRL1 and TRV2::GhPIN8 had a reduced root length, surface area. Moreover, the contents of cis-12-oxo-phytodienoic acid (cis-OPDA), isopentenyl adenosine (iPR) and cis-zeatin (cZ) in the roots of the plants expressing TRV2::GhTRL1 decreased. This study contributes to the cultivation and improvement of cotton varieties. [ABSTRACT FROM AUTHOR]

A hydroponic experiment was conducted to explore the effects of nitrogen on cotton root morphology and related hormone contents and to analyse the correlation between the indexes. The effects of different nitrogen concentrations (N0, N1, N2, and N3 with 0, 2, 4, and 8 mmol l−1, respectively) on main and lateral roots were evaluated. A moderate nitrogen concentration (N2, 4 mmol l−1) promotes root growth. Lateral roots responded quickly to changes in nitrogen concentrations. Compared with N0 treatment, N2 treatment resulted in significantly greater main root volume after 12 days as well as increased lateral root length, root projected area, root surface area, and root volume after 8 days. Nitrogen significantly decreased abscisic acid (ABA), salicylic acid (SA), and isopentenyladenine (iP) content, which were the lowest in N2 treatment (33.92% lower than N0). The ABA and SA content were negatively correlated with root morphology. This shows that a moderate nitrogen concentration (4 mmol l−1) significantly decreased ABA and SA content in the main and lateral roots and promoted root growth in cotton plants. These results will contribute to root growth theory regarding efficient nitrogen utilization by cotton plants and will provide a theoretical basis to ensure nitrogen resources are utilized efficiently. [ABSTRACT FROM AUTHOR]

Allocation of newly formed biomass towards plant organs is a key determinant of plant performance that is affected by agronomic practices such as plant population density and use of growth regulators. Here we quantified biomass allocation of intercropped cotton ( Gossypium hirsutum ) growing at two population densities (3.0 and 7.5 plants m −2 ) and with or without application of the growth regulator mepiquat chloride (MC) in three consecutive years. The beta growth function was used to quantitatively characterize the dynamics of biomass partitioning. Compared to low density, high density increased daily growth rate and final above-ground dry matter, but decreased allocation to fruits. Application of MC did not affect dry matter accumulation but increased allocation to fruits by 22%. The parameters of the beta growth function have a clear biological interpretation, providing a useful quantitative characterization of the effect of management on dry matter allocation in cotton. The function may also be used to model organ-specific daily assimilate partitioning as a component in models of plant growth and crop production with the consideration of discussed caveats. [ABSTRACT FROM AUTHOR]

Highlights: [•] Plant growth regulator mepiquat chloride (MC) significantly reduced plant height and length of branches. [•] Increasing plant density significantly increased crop light use efficiency, especially during the reproductive phase. [•] At high plant densities, MC improved plant architecture, resulting in a higher light use efficiency and yield. [Copyright &y& Elsevier]