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[Display omitted] • In this study, the genome of one perennial Gb cotton accession was assembled leading to identify intraspecific and interspecific SVs associated with the agronomic traits. • Haploblocks in sea-island cotton were associated with agronomic traits improvement and drove the differentiation and adaptation of sea-island cotton. • Our study builds a foundation for the breeding and improvement of sea-island cotton. Sea-island cotton (Gossypium barbadense , Gb) is one of the major sources of high-grade natural fiber. Besides the common annual Gb cotton, perennial Gb cotton is also cultivated, but studies on perennial Gb cotton are rare. We aimed to make a systematic analysis of perennial sea-island cotton and lay a foundation for its utilization in breeding, and try to identify the representative structural variations (SVs) in sea-island cotton, and to reveal the population differentiation and adaptive improvement of sea-island cotton. Through genome assembly of one perennial Gb cotton accession (named Gb_M210936) and comparative genome analysis, variations during Gb cotton domestication were identified by comparing Gb_M210936 with annual Gb accession 3–79 and with wild allotetraploid cotton G. darwinii. Six perennial Gb accessions combining with the resequenced 1,129 cotton accessions were used to conduct population and genetic analysis. Large haplotype blocks (haploblocks), generated from interspecific introgressions and intraspecific inversions, were identified and were used to analyze their effects on population differentiation and agronomic traits of sea-island cotton. One reference genome of perennial sea-island cotton was assembled. Representative SVs in sea-island cotton were identified, and 31 SVs were found to be associated with agronomic traits. Perennial Gb cotton had a closer kinship with the wild-to-landrace continuum Gb cotton from south America where Gb cotton is originally domesticated. Haploblocks were associated with agronomic traits improvement of sea-island cotton, promoted sea-island cotton differentiation into three subgroups, were suffered from breeding selection, and may drive Gb cotton to be adapted to central Asian. Our study made up the lack of perennial Gb cotton genome, and clarified that exotic introgressions improved the traits of sea-island cotton, promoted the population differentiation, and drove sea-island cotton adaptive to central Asia, which will provide new insights for the genetic breeding improvement of sea-island cottons. [ABSTRACT FROM AUTHOR]

High-resolution 2D and 3D seismic data are used to investigate the morphology, internal architecture and origin of widespread seafloor undulations in the eastern area of a submarine canyon system, northern South China Sea. The seafloor undulations reveal similar seafloor morphologies, and three different types (Types A, B and C) can be classified based on their relative locations and internal seismic characters. Types A and B are observed in the canyon areas, whereas Type C occurs in the canyon heads. Seismic reflections within Types A and C are continuous and have an upslope migrating trend, while Type B seafloor undulations are separated by listric faults. Our analysis reveals the origins of these three different types of seafloor undulations. Type A seafloor undulations are sediment waves formed by turbidity currents flowing through the submarine canyons. Gravity-driven submarine creep resulted in the formation of Type B seafloor undulations. Type C undulations are sediment waves generated by internal waves interacting with the continental slope. Our results provide information about the origin of widespread seafloor undulations in other submarine canyon systems. It is also of great significance to future risk assessments, as the study area now is one of the most active regions for hydrocarbon exploration in SE Asia. • Widespread seafloor undulations are identified on the South China Sea margin. • Three types of seafloor undulations show different morphology and internal character. • Different processes are responsible for the generation of the seafloor undulations. • Correctly identifying their origin is important for future geohazard assessments. [ABSTRACT FROM AUTHOR]