Foliar and seed application of plant growth regulators affects cotton yield by altering leaf physiology and floral bud carbohydrate accumulation

Abstract

The development of cotton (Gossypium hirsutum L.) floral bud prior to flowering is fundamental for yield formation since it is the initial step in the fruiting cycle. However, little information is available on the early reproductive stage of cotton subjected to plant growth regulators (PGRs). A 2-year experiment was conducted to investigate the effects of gibberellic acid (GA3), N6-benzyladenine (6-BA) and N, N-dimethyl piperidinium chloride (DPC) with two application methods [(A) seed soaking and (B) foliar spraying at squaring stage] on cotton floral bud development, yield and yield components compared with the control (water application). The results showed that seedcotton yield increased by 6.3%–7.5% and 12.1%–13.3% respectively in GA3 and 6-BA seed soaking treatments, and by 7.7%–8.5% and 8.2%–11.0% after foliar application compared to control due to increased boll numbers, which were associated with higher floral bud numbers. However, there was no response to yield for DPC treatment. Additionally, GA3 and 6-BA significantly increased photosynthesis rate (Pn) accordingly affecting the subtending leaf carbohydrate content and translocation, resulting in higher sucrose and starch contents in floral buds, which substantially enhanced dry matter of floral buds and reduced abscission rate. Those responses in floral buds are conductive to favorable boll development, which was evidenced by higher boll retention and boll opening rate for GA3 and 6-BA application relative to control. Specially, 6-BA showed equal effects to GA3 on yield and yield components with application method B, whereas induced a greater promotion than GA3 with application method A in the following aspects: (1) square numbers, boll numbers and seedcotton yield increased more obviously under 6-BA than GA3; (2) the increases in boll retention and boll opening rate were larger under 6-BA than GA3; (3) 6-BA induced higher carbohydrate content in floral buds than GA3.