Carpel-Specific Suppression of GhCKX3b Enhances Cotton Yield Without Compromising Fiber Quality in the Elite Cultivar ‘Yuanmian 8’

Improving cotton yield without sacrificing fiber quality remains a major breeding challenge. In this study, a carpel-specific RNA interference construct targeting GhCKX3b was introduced into the elite upland cotton cultivar ‘Yuanmian 8’, which has high fiber quality but relatively low lint percentage. We evaluated the effects of this construct on cytokinin accumulation, yield-related traits, and fiber quality across T0, T1, and T2 generations. Carpel-specific suppression of GhCKX3b increased cytokinin content in T2 positive lines by 50.3% to 102.0% relative to wild-type. Transgenic lines consistently showed increased lint percentage, boll weight, and seeds per boll, while seed index decreased moderately. In the best-performing line, lint percentage increased from 36.4% to 45.8%, and boll weight from 6.30 g to 7.31 g. Multi-year field evaluations confirmed stable inheritance of these improvements across generations. Importantly, major fiber quality parameters—including length, strength, and micronaire—remained within high-quality cotton standards. These results indicate that carpel-specific GhCKX3b suppression effectively improves key yield components in a high-quality cotton background without compromising fiber quality. This study provides breeding-oriented evidence supporting the application of tissue-specific cytokinin regulation in cotton improvement.