Waxy maize has many excellent characteristics in terms of its nutritional and economic value. In recent decades, the waxy maize germplasm has increased dramatically as a result of different selection methods. We collected 200 waxy maize inbred accessions from different origins to study their genetic diversity and phylogenetic relationships, and to identify new waxy mutations. A simple sequence repeat (SSR) analysis revealed wide genetic diversity among the 200 waxy maize accessions. The maize accessions were clustered into three groups. We sequenced the waxy gene from the first to the 14th exon. Nucleotide variation analysis of 167 waxy maize and 14 flint maize lines revealed some nucleotide differences in the waxy gene among different waxy maize groups, and much narrower nucleotide diversity in waxy maize than in flint maize. In a phylogenetic analysis, waxy maize carrying the same mutation allele clustered together, and waxy maize carrying different mutation alleles distributed in different groups; waxy maize was intermixed with flint maize in each branch, and wx-D7 waxy maize separated significantly from waxy maize lines carrying wx-D10, wx-124 and wx-hAT mutant alleles. The wx-hAT was a new waxy mutation identified in this study. It consisted of a 2286-bp transposon inserted into the middle of exon three of the waxy gene. A PCR marker specific for the wx-hAT allele was developed. These results will be useful for the utilization and preservation of the waxy maize germplasm, and the PCR marker has potential uses in waxy maize breeding programs.
The Ordovician Wulalike marine siliceous shale is a notable hydrocarbon source rock in the Northwestern Ordos Basin. However, the causes of quartz and organic matter enrichment are still a mystery to experts. In this study, the organic geochemistry (maceral compositions, Rbitu, and TOC) and elemental geochemistry (major and trace elements) with mineralogy (XRD) and petrography were jointly acquired to systematically investigate the quartz origins and the paleoenvironment, and the main controlling factors for organic matter enrichment in the Wulalike shale. The results show that the organic matter is type I kerogen with low TOC concentrations (average 0.51%), and that the thermal evolution has reached mature and high mature stages (mean Requ is 1.08%). Three types of quartz are developed in Wulalike shale: biogenic quartz (average 63%) is the most dominant, followed by clastic quartz (average 31%) and microcrystalline quartz (average 6%). Babio and Ba/Al values indicate the low paleoproductivity, which is the primary cause for the low TOC found throughout the area. Redox indexes show the anoxic or dysoxic to oxic conditions from the bottom to the top of the section. Paleoclimate and paleowater depth proxies also changed from the bottom to the top. Various paleoenvironments and sedimentological evidence show that Wulalike shale went through the changing environments, and the early sedimentary environments were conducive to organic matter enrichment, leading to a relatively high TOC. The paleoproductivity and preservation conditions have an impact on organic matter enrichment. Based on the results of biogenic quartz distribution and sedimentary environments, it is considered that the bottom of the Wulalike Formation is the most favorable for shale gas exploration and development.
At the south‐western margin of the North China Craton (NCC), there existed a lot of Mesoproterozoic strata. However, it is hardly known about the Mesoproterozoic stratigraphic sequence and deep structures of the south‐western part of NCC (most is the Ordos Block) due to the thick Phanerozoic sedimentary cover above the Precambrian basement and strata. Combining the drilling well data, seismic profiles, and outcrops around the whole Ordos Block, it becomes possible to reveal the deep structure and distribution of Mesoproterozoic strata. The distribution and sedimentation of Mesoproterozoic at the southwestern margin of NCC were controlled by a series of NE–SW extension deep faults just existed in Mesoproterozoic Changcheng System and Jixian System. According to the drilling well data, the Changchang System includes several various thickness volcanic rocks, and the stratigraphic sequence and lithological combination are similar to the Yanliao Rift. During the sedimentation from Longjiayuan Formation to Duguan Formation, the water got deeper revealed by the content of Ce element gradually decreasing. However, the content of Ce element unusually increases during the steady subsidence of the Mesoproterozoic basin, while the Xunjiansi Formation sedimented. The deposition of tephra or hydrothermal might contribute a lot to the increase of the Ce element's content. Besides that, numerous soft‐sediment deformation structures developed in carbonate rocks of Mesoproterozoic Xunjiansi Formation at the south‐western margin of NCC. What's more, the Xunjiansi Formation with soft‐sediment deformation structures can be regarded as a marker bed for the comparison with the Wumishan Formation in Yanliao Rift. Besides that, there is a set of residual sandstone conformably covered the dolomite of Mesoproterozoic Fengjiawan Formation. It corresponds with Xiamaling Formation of Building System in Yanliao Rift System based on the stratigraphic sequence and relative sedimentary time limited by the youngest zircon U–Pb age peak 1,511.1 ± 10 Ma (n = 7) and single zircon U–Pb age 1,436 ± 28 Ma. Therefore, the south‐western part of NCC have high similarity of stratigraphic sequence and sedimentary framework with Yanliao Rift. Moreover, the development of volcanic rocks in Changcheng System, soft‐sediment deformation structures, and Ce abnormal increasing in Xunjiansi Formation might suggest that there developed an active Mesoproterozoic Rift in the south‐western part of the NCC similar to Yanliao Rift. Generally, the south‐western part of NCC share similar tectonic background with Yanliao Rift.
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