Agronomic and Fibre Quality Assessment of Cotton Breeding Lines Under Verticillium Wilt Conditions

The aim of the study was to identify promising cotton samples with high yield, adaptability, and stable fibre quality. The present work presents the results of a comprehensive assessment of 91 breeding samples of cotton according to economically valuable and technological traits under the conditions of southern Kazakhstan and Uzbekistan in 2024. The comparative analysis identified several promising samples, with M-4010, M-4015, M-4017, M-4019, and M-4025 selected as priority lines. Across the station, competitive, and infectious trials, the breeding samples showed yields of 32.5-46.8 c/ha, fibre output of 36.3-39.8%, fibre length of 32.6-33.7 mm, and fibre breaking load of 4.4-5.6 gf. The study included samples with different genetic predispositions to stresses and to Verticillium dahliae infection, including the variety M-4005 as a control standard and the variety S-4727 as a susceptible benchmark. For the assessment of agronomic and technological characteristics, field and laboratory analyses were used, including measurement of the vegetation period, yield, boll structure, fibre output, fibre breaking load, micronaire, and maturity. At the station-trial stage, the samples had vegetation periods of 118-129 days, yields of 36.2-46.8 c/ha compared with 38.4 c/ha in M-4005, boll mass of 5.6-6.2 g, and fibre output of 36.4-39.1%. The evaluated lines had fibre length of up to 33.7 mm, micronaire values of 4.6-4.8, fibre breaking loads of 5.3-5.6 gf, and fibre metric numbers of 5,240-5,490 m/g. The reliability of the differences between genotypes was confirmed by the ANOVA method at a significance level of p<0.05. The infectious variety trial at a pathogen concentration of ≥10⁵ CFU/g of soil showed total wilt incidence of 0.0-0.9% in all 40 new breeding lines, compared with 0.7% in M-4005 and 37.4% in S-4727. Under the infectious background, fibre breaking load ranged from 4.4 to 5.0 gf, micronaire from 4.4 to 4.8, fibre metric number from 5,260 to 5,640 m/g, and fibre breaking length from 24.6 to 26.3 km. The practical value of this study lies in the identification of highly productive cotton samples showing a high level of field resistance under the tested Verticillium dahliae infectious background and suitable for further evaluation in breeding programmes.