Comparative per formance of hybrid generations reveals the potential application of -F2 hybrids in upland cotton

Background: The utilization of heterosis has greatly improved the productivity of cotton worldwide. However, a major constraint for the large-scale promotion of -F1 hybrid cotton is artificial emasculation and pollination. This study proposed the potential utilization of -F2 hybrids to improve upland cotton production through a comparative evalua-tion of hybrid generations. Results: Eight upland cotton varieties were analyzed and crosses were made according to NCⅡ incomplete diallel cross-breeding design in two cotton belts of China. Variance analysis revealed significant differences in agronomic, yield, and fiber quality in both generations and environments. The broad-sense heritability of agronomic and yield traits was relatively higher than quality traits. Furthermore, the narrow-sense heritability of some traits was higher in -F2 than in the -F1 generation in both cotton belts. Overall, parental lines Zhong901, ZB, L28, and Z98 were observed with maximum combining ability while combinations with strong special combining ability were ZB × DT, L28 × Z98, and ZB × 851. The yield traits heterosis was predominant in both generations. However, the level of heterosis was altered with trait, hybrid combination, generation, and environment. Interestingly, L28 × Z98 performed outstandingly in Anyang. Its lint yield (LY) was 24.2％ higher in -F1 and 11.6％ in -F2 than that of the control Ruiza 816. The performance of SJ48 × Z98 was excellent in Aral which showed 36.5％ higher LY in -F1 and 10.9％ in -F2 than control CCRI 49. Further results revealed most hybrid combinations had shown a low level of heterosis for agronomic and fiber quality traits in both generations. Comparatively, ZB × DT and L28 × Z98 showed hybrid vigor for multiple traits in both generations and cotton belts. It is feasible to screen strong heterosis hybrid combinations with fine fiber in early generations. In the two environments, the correlation of some traits showed the same trend, and the correlation degree of Anyang site was higher than that of Aral site, and the correlation of some traits showed the opposite trend. According to the performance of strong heterosis hybrid combinations in different environments, the plant type, yield and fiber traits associated with them can be improved according to the correlation. Conclusions: Through comparative analysis of variance, combining ability, and heterosis in -F1 and -F2 hybrids in dif-ferent cotton belts, this study proposed the potential utilization of -F2 hybrids to improve upland cotton productivity in China.