Gibberellin-induced Stem Elongation and Apical Bud Growth Acceleration Without Decreased Yield in Broccoli (<i>Brassica oleracea</i> L. var. <i>Italica</i>)

Abstract

In Japan, broccoli (Brassica oleracea L. var. Italica) is primarily harvested manually. Some Japanese broccoli cultivars have short stems, but these broccoli heads are more difficult to harvest, and complicate the introduction of mechanical harvesters. Therefore, research is focused on strategies to control stem length. The present study examined the effects of the plant hormone gibberellin (GA) on the morphological and agronomic traits of broccoli shoots. The broccoli cultivar ‘SK9-099’, widely distributed in Japan and characterized by a short stem, was studied. These experiments were conducted over three cropping seasons, i.e., spring (Exp. 1), summer (Exp. 2), and fall (Exp. 3), with four GA treatment plots at 0 ppm (Control), 20 ppm, 100 ppm, and 500 ppm. This study observed that, on average, GA elongated stem length from approximately 16.0 cm in the control plot to 24.7 cm in the 500 ppm plot for the three cropping seasons, without decreasing yield. In addition, GA treatment accelerated apical bud growth and shortened the overall growth period by 16 days in the 500 ppm plot compared to the control in the fall, equivalent to 20.5% of the growth period from transplantation to harvest in the latter.This study highlights several practical benefits of GA application for growers, minimizing manual harvesting labor, avoid the difficult of designing mechanical harvesters for short-stemmed cultivars, and increase field usage efficiency by shortening the growth period.