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Salinity stress is one of the primary threats to agricultural crops resulting in impaired crop growth and development. Although cotton is considered as reasonably salt tolerant, it is sensitive to salt stress at some critical stages like germination, flowering, boll formation, resulting in reduced biomass and fiber production. The mechanism of partial ion exclusion (exclusion of Na+ and/or Cl–) in cotton appears to be responsible for the pattern of uptake and accumulation of harmful ions (Na+ and Cl) in tissues of plants exposed to saline conditions. Maintaining high tissue K+/Na+ and Ca2+/Na+ ratios has been proposed as a key selection factor for salt tolerance in cotton. The key adaptation mechanism in cotton under salt stress is excessive sodium exclusion or compartmentation. Among the cultivated species of cotton, Egyptian cotton (Gossypium barbadense L.) exhibit better salt tolerance with good fiber quality traits as compared to most cultivated cotton and it can be used to improve five quality traits and transfer salt tolerance into Upland or American cotton (Gossypium hirsutum L.) by interspecific introgression. Cotton genetic studies on salt tolerance revealed that the majority of growth, yield, and fiber traits are genetically determined, and controlled by quantitative trait loci (QTLs). Molecular markers linked to genes or QTLs affecting key traits have been identified, and they could be utilized as an indirect selection criterion to enhance breeding efficiency through marker-assisted selection (MAS). Transfer of genes for compatible solute, which are an important aspect of ion compartmentation, into salt-sensitive species is, theoretically, a simple strategy to improve tolerance. The expression of particular stress-related genes is involved in plant adaptation to environmental stressors. As a result, enhancing tolerance to salt stress can be achieved by marker assisted selection added with modern gene editing tools can boost the breeding strategies that defend and uphold the structure and function of cellular components. The intent of this review was to recapitulate the advancements in salt screening methods, tolerant germplasm sources and their inheritance, biochemical, morpho-physiological, and molecular characteristics, transgenic approaches, and QTLs for salt tolerance in cotton.

Plant cytochrome P450 (P450) participates in a wide range of biosynthetic reactions and targets a variety of biological molecules. These reactions lead to various fatty acid conjugates, plant hormones, secondary metabolites, lignin, and various defensive compounds. In our previous research, transcriptome analysis was performed on the salt-tolerant upland cotton “Tongyan No. 1.” Many differentially expressed genes (DEGs) belong to the P450 family, and their domains occur widely in plants. In this current research, P450 genes were identified in Gossypium hirsutum with the aid of bioinformatics methods for investigating phylogenetic relations, gene structure, cis-elements, chromosomal localization, and collinearity within a genome. qRT-PCR was conducted to analyze P450 gene expression patterns under salt stress. The molecular weights of the 156 P450 genes were in the range of 5,949.6–245,576.3 Da, and the length of the encoded amino acids for all the identified P450 genes ranged from 51 to 2,144. P450 proteins are divided into four different subfamilies based on phylogenetic relationship, gene structure, and chromosomal localization of gene replication. The length of P450 genes in upland cotton differs greatly, ranging from 1,500 to 13,000 bp. The number of exons in the P450 family genes ranged from 1 to 9, while the number of introns ranged from 0 to 8, and there were similar trends within clusters. A total of 31 cis-acting elements were identified by analyzing 1,500 bp promoter sequences. Differences were found in cis-acting elements among genes. The consistency between qRT-PCR and previous transcriptome analysis of salt tolerance DEGs indicated that they were likely to be involved in the salt tolerance of cotton seedlings. Our results provide valuable information on the evolutionary relationships of genes and functional characteristics of the gene family, which is beneficial for further study of the cotton P450 gene family.

Cotton is an important fiber and cash crop. Extreme water scarceness affects the growth, quality, and productivity of cotton. Water shortage has threatened the future scenario for cotton growers, so it is imperative to devise a solution to this problem. In this research, we have tried to machinate a solution for it. 23 genotypes have been screened out against drought tolerance at the seedling stage by evaluating the morphological, physiological, and biochemical traits in a triplicate completely randomized design plot experiment with two water regimes [50 and 100% field capacity]. Genotypic differences for all the morphological and physiological traits revealed highly significant differences except transpiration rate (TR). Moreover, the interaction between genotype and water regime (G × W) was highly significant for root length (RL, 5.163), shoot length (SL, 11.751), excised leaf water loss (ELWL, 0.041), and stomatal conductance (SC, 7.406). A positively strong correlation was found in TR with relative water content (RWC; 0.510) and SC (0.584) and RWC with photosynthesis (0.452) under drought conditions. A negative correlation was found in SC with SL (−0.428) and photosynthesis (−0.446). Traits like RL, SL, SC, photosynthesis, proline, catalase, and malondialdehyde were visible indicators, which can differentiate drought-tolerant genotypes from the susceptible ones. A wide range of diversity was found in all the morpho-physiological traits with the cumulative variance of four principal components (PCs) 83.09% and three PCs 73.41% under normal and water-stressed conditions, respectively, as per the principal component analysis. Hence, selection criteria can be established on the aforementioned traits for the development of drought-tolerant cultivars. Moreover, it was found that out of 23 experimental varieties, NIAB-135, NIAB-512, and CIM-554 could be used to devise breeding strategies for improving drought tolerance in cotton.