Effect of the mode and time of gibberellic acid treatment on plant architecture and bulb structure in garlic (Allium sativum L.)

Abstract Garlic (Allium sativum L.) bulb, as the main propagation organ, is consumed worldwide for its flavor and medicinal value. Our previous work showed that injecting plant with gibberellic acid (GA3) can dramatically increase the clove number per bulb to improve propagation efficiency of garlic. However, how the mode and time of application of GA3 affect plant architecture and bulb structure remains largely unknown. Herein, we investigated the effect of both soaking seed clove in GA3 solution for different durations (6, 12, 24 and 48 h, respectively) and injecting plant with GA3 at seven growth stages (30, 60, 90, 120, 150, 180 and 210 days after planting) on plant growth and bulb development in garlic cultivar G024. It was evident that soaking seed clove in GA3 solution for 48 h induced secondary plant (equated with tiller or lateral branch) formation and significantly increased the incidence rate of secondary plant, clove number per bulb and bulb weight. In 2016–2017 and 2017–2018, clove number per bulb (19.59 and 19.64, respectively) and bulb weight (50.72 g and 48.82 g, respectively) were sharply increased by injection of GA3 at 30 days after planting (DAP), as compared to control (12.14 and 11.75, respectively; 37.53 g and 36.72 g, respectively). No difference in clove number per bulb among control, “GA3 180 DAP” and “GA3 210 DAP” was recorded. Furthermore, soluble sugar content in stem was higher at 4 days after GA3 treatment and was lower at 32 days after GA3 treatment, as compared to control. At 8, 16 and 32 days after GA3 treatment, soluble protein content in stem (4.28, 4.55 and 7.32 mg g−1 FW, respectively) was always higher than control (2.52, 3.44 and 5.81 mg g−1 FW, respectively). In summary, soaking seed clove in 1 mM L−1 GA3 solution for 48 h is a better way to increase bulb weight but caused a decrease in bulb commodity quality. While injecting plant with 1 mM L−1 GA3 at 60, 90 or 120 DAP can be used for increasing clove number per bulb to improve propagation efficiency of garlic. Exogenous GA3 induced axillary bud formation of garlic via the changes of soluble sugar content and soluble protein content in stem.