Foliar application of silicon and boron improves boll retention, lint yield and fiber quality traits of transgenic cotton

Background: Cotton (Gossypium hirsutum L.) is an important fiber crop that has a widespread cultivation in tropical and subtropical regions globally. The decline in cotton production over the last two decades may be attributed to the effects of climate change and imbalances in mineral nutrition. However, mineral nutrition, particularly micronutrients has been less focused in cotton production. Silicon (Si) and boron (B) are considered crucial micronutrients that play diverse functions in the physiological and biochemical development of plants, as well as in enhancing their resistance to abiotic stress. Methods: The present study investigated the impact of individual and combined foliar application of Si and B on the development of transgenic (Bt) cotton, as well as their impacts on boll retention, seed cotton production, and fiber quality indicators. Treatments included individual application of 2.0- and 4.0-mM Si and 0.5- and 1.0-mM B, and combined application 2.0 mM Si + 0.5 mM B, 2.0 mM Si + 1.0 mM B, 4 mM Si + 0.5 mM B and 4.0 mM Si + 1.0 mM B. Water spray and no foliar application were regarded as controls for comparison. Results: Combined application of 4 mM Si + 1.0 mM B resulted in the highest ginning out turn (39%), fiber uniformity (83%) and fiber length (28 mm). The longest plant height and the highest number of closed bolls per plant were recorded with sole application of 0.5 mM B, while sole application of 1 mM B produced the highest number of monopodial branches (20.26), sympodial branches (33.53) and total number of bolls (37.03) per plant. The highest boll weight (18.39 g), boll retention (64.38%) and seed cotton yield (1253.7 kg ha−1) were recorded for sole application of 1.0 mM B. Conclusion: The results revealed that combined foliar application of 4.0 mM Si + 0.5 or 1.0 0.5 mM fiber quality traits, whereas sole application of 1.0 mM B improved growth and yield related traits. Therefore, B and Si can be applied in combination to improve the fiber quality, whereas sole application of B could increase yield-related traits.