| Soil salinity is a serious problem in the arid southwestern and western regions of the Unites States where cotton is extensively grown. Salinity stress causes a series of negative effects on cotton growth, yield, and fiber quality. Therefore, identification and development of salt-tolerant cotton genotypes is an important aspect for further improvement in cotton production under saline conditions. The objectives of this study were to identify salt-tolerant genotypes from backcross inbred lines (BILs) developed from Upland (Gossypium hirsutum) x Pima (G. barbadense ) at the seed germination and seedling stages under 200 mM NaCl and control (no salt) conditions; to develop molecular markers related to salt tolerance; and to identify quantitative trait loci (QTL) for the genetic control of salt tolerance in cotton. Based on reduction in seed germination, Pima S-7 was found to be more highly tolerant than Upland SG 747. The BIL population exhibited a higher level of variability in seed germination under the salt stress conditions that allowed the identification of salt tolerant and salt sensitive lines at seed germination.;Contrary to seed germination, Pima S-7 was somewhat sensitive to salt at the seedling growth stage than Upland SG 747. However, based on percent reduction in seedling growth characteristics there was no significant difference between the two parents. Based on percent reduction of the traits measured, several BIL genotypes performed better than both parents, allowing identification of breeding lines with improved salt tolerance at the seedling stage.;To develop molecular markers related to salt tolerance, two cultivated tetraploid cotton species Upland and Pima cotton, and their progenitor diploid species G. arboreum and G. raimondii, together with 93 BILs were surveyed for single nucleotide polymorphism (SNP) based on single strand conformation polymorphism (SSCP) technique on salt stress responsive genes. Out of 152 primer pairs, 73 primer pairs produced 212 inter- and intra-specific polymorphic SSCP markers among the four cotton species. However, only 55 primers yielded 118 polymorphic markers in the BILs, 64 of which were significantly correlated with the phenotypic traits.;To identify quantitative trait loci (QTLs) for salt tolerance in cotton, a linkage map was constructed using various marker systems including SSCP markers. Of 645 markers, a total of 287 markers were placed on 44 linkage groups that spanned 978.7 cM of the cotton genome. Of the 118 SSCP markers, 47 were mapped onto 16 linkage groups and 27 of the mapped SSCP markers were significantly correlated with various phenotypic traits. A total of six QTLs were identified, including three for plant height, one for leaf number, one for root fresh weight, and one for root dry weight. Also, one epistatic QTL was detected for root dry weight. This study has provided improved germplasm, gene-based markers and QTLs for salt tolerance and will facilitate marker-assisted breeding for salt tolerance in cotton. |
