Objective To identify the salinity-alkali tolerance of Gossypium hirsutum race Latifolium 32, CRI 12, and their derived F₉ RIL population, screen elite salinity-alkali tolerant cotton lines, excavate high-quality salinity-alkali resistant cotton germplasm resources, and provide theoretical reference for breeding new salinity-alkali tolerant cotton cultivars.

Methods A total of 270 test materials, including 2 parental lines and 268 F₉ RIL lines developed by crossing Gossypium hirsutum race Latifolium 32 (female parent) with CRI 12 (male parent), were planted in natural saline-alkali fields. Agronomic traits (seedling emergence rate, boll number, fruiting branch number, lint percentage, plant height), yield components (single boll weight, seed cotton yield per plant, lint yield per plant), and fiber quality indices (Micronaire value, fiber breaking tenacity, upper-half mean length, fiber uniformity index, fiber elongation) were measured. The membership function method combined with cluster analysis was adopted to comprehensively evaluate the salinity-alkali tolerance of all materials.

Results Saline-alkali stress mainly restrained agronomic and yield traits, among which plant height was inhibited most significantly; fiber quality was barely affected. Gossypium hirsutum race Latifolium 32 exhibited stronger salinity-alkali tolerance than CRI 12, and continuous phenotypic variation of salinity-alkali tolerance was observed in the RIL population.

Conclusion Gossypium hirsutum race Latifolium 32 possesses superior salinity-alkali tolerance compared with CRI 12. Saline-alkali stress mainly reduces plant height, fruiting branch number and boll number, shortens the boll opening period, and significantly raises the fiber Micronaire value (i.e., increased fiber fineness and maturity). Easily surveyed traits including plant height, fruiting branch number and boll number can serve as core indicators for rapid evaluation of salinity-alkali tolerance in upland cotton. A total of 39 highly salinity-alkali tolerant lines and 35 saline-alkali sensitive lines were screened out in this study.