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(1) Background: Upland cotton (Gossypium hirsutum L.) is the most important natural fiber worldwide, and it is extensively planted and plentifully used in the textile industry. Major cotton planting regions are frequently affected by abiotic stress, especially drought stress. Drought resistance is a complex, quantitative trait. A genome-wide association study (GWAS) constitutes an efficient method for dissecting the genetic architecture of complex traits. In this study, the drought resistance of a population of 316 upland cotton accessions was studied via GWAS. (2) Methods: GWAS methodology was employed to identify relationships between molecular markers or candidate genes and phenotypes of interest. (3) Results: A total of 8, 3, and 6 SNPs were associated with the euphylla wilting score (EWS), cotyledon wilting score (CWS), and leaf temperature (LT), respectively, based on a general linear model and a factored spectrally transformed linear mixed model. For these traits, 7 QTLs were found, of which 2 each were located on chromosomes A05, A11, and D03, and of which 1 was located on chromosome A01. Importantly, in the candidate regions WRKY70, GhCIPK6, SnRK2.6, and NET1A, which are involved in the response to abscisic acid (ABA), the mitogen-activated protein kinase (MAPK) signaling pathway and the calcium transduction pathway were identified in upland cotton at the seedling stage under drought stress according to annotation information and linkage disequilibrium (LD) block analysis. Moreover, RNA sequencing analysis showed that WRKY70, GhCIPK6, SnRK2.6, and NET1A were induced by drought stress, and the expression of these genes was significantly different between normal and drought stress conditions. (4) Conclusions: The present study should provide some genomic resources for drought resistance in upland cotton. Moreover, the germplasm of the different phenotypes, the detected SNPs and, the potential candidate genes will be helpful for molecular marker-assisted breeding studies about increased drought resistance in upland cotton.

Rapid expansion of leaves of early-stage plants in wheat produced by chromosomal control of characteristics related to rapid expansion of the first six leaves of wheat were investigated using a set of single chromosome substitution lines under two different temperature regimes (TRs). Results from this study indicated that several chromosomes could be responsible for each of the four characteristics studied (including leaf width, leaf length, leaf elongation rate and leaf appearance index) and that different chromosomes may be responsible for the same characteristics at different TRs. Only a small number of substitutions that showed the most significant effects on leaf length were found among those that showed the most significant effects on leaf width, providing further evidence that these two characteristics are likely controlled by different sets of genes. Substitutions 4B, 4D, and 5A are among those that were repeatedly detected to having significant effects on different leaf characteristics at the lower-TR and genes residing on these three chromosomes could be homologous. This possibility and its implication are discussed.