Response of Selected Tetraploid Gossypium Species to Salt.

Cotton is considered to be a moderately sensitive crop to salinity with a 7.7 dS m–1 threshold; however its yield, quality, and germination are affected by different salinity levels. Identification of additional salt-tolerance in cotton germplasm resources is important for improvement in cotton production. Because wild Gossypium hirsutum, G. tomentosum, and G. darwinii were distributed by ocean currents, we hypothesized that they would be more resistant to salt water than cultivated G. hirsutum. The objective of this study was to determine the phenotypic effect of salt on cotton and identify salt-tolerant genotypes of Gossypium under salt stress. Three wild tetraploid species, G. hirsutum, G. tomentosum, and G. darwinii, were utilized for identification of salt-tolerance compared to cultivated G. hirsutum. Experiments for phenotypic effect of salinity were conducted at germination in five NaCl concentrations (50, 100, 125, 200, & 250 mM NaCl) and at the seedling stage (4 weeks after germination) at 250 mM NaCl. Germination of G. tomentosum was completely inhibited at more than 125 mM NaCl while G. darwinii was severely inhibited (>72%) at this concentration, whereas, the accessions of G. hirsutum were inhibited only about 33% or less at this concentration. Surprisingly, at the seedling stage the wild G. hirsutum accessions were more sensitive to salt than the cultivated genotypes. Leaf area, shoot length, root length, shoot and root fresh weight were decreased by salinity. Leaf damage and plant death were the major observable responses of the plants at 250 mM NaCl. Plant death was most common in G. darwinii. Root length of cultivated G. hirsutum (444RB and DP33B) was increased by salinity, however, shoot and root fresh weight were decreased in all three species. Cultivated (ST 444RB, DP33B) and wild G. hirsutum (LMK-4) were the most resistant to salt at germination and at 4 weeks after germination.