Onion (Allium cepa L.) is one of the most important vegetable crops worldwide. In Japan, it is grown using two different cultivation methods (spring-sowing and autumn-sowing). The traditional cultivation method for onion in the Tohoku region in northeast Japan has been autumn sowing; however, onion productivity has been low. Recently, spring sowing of onion has been established in this region to improve onion productivity in the off-crop season. To better understand the spring-sowing cultivation method, we examined the plant growth and bulb development of eight commercially-grown onion cultivars (‘Turbo’, ‘Aurora’, ‘Momiji No. 3’, ‘Marso’, ‘Okhotsk 222’, ‘Kitamomiji 2000’, ‘Super Kitamomiji’, and ‘Gunnison’) throughout the growth period. The results showed that this cultivation method enabled us to grow and compare relatively long-day and intermediate-day cultivars at the same time, under the same environmental conditions. Onion bulb development was induced and persisted during long day-lengths and was inhibited by short day-lengths which were longer or shorter than the critical day-lengths for bulb development of each cultivar. To elucidate this mechanism, expression analysis of AcFTs related to bulb development was conducted. Our expression analysis showed that AcFT1 was expressed in accordance with the maturity of the cultivars, and this gene expression can be used as an index for maturity types of the cultivars and bulb development. The results indicate that onion responds to a critical day-length for bulb development and starts bulb development before the bulbing ratio greatly exceeds 2. This metric can be used as an index of bulb development.

洋葱（洋葱）L.）是世界上最重要的蔬菜作物之一。在日本，使用两种不同的栽培方法（春播和秋播）进行种植。日本东北东北地区的传统洋葱栽培方法是秋季播种。但是，洋葱的生产率很低。最近，已经在该地区建立了葱春播种，以提高非农季节的洋葱生产力。为了更好地了解春播栽培方法，我们研究了8种商业种植洋葱品种（“ Turbo”，“ Aurora”，“ Momiji No.3”，“ Marso”，“ Okhotsk 222”，在整个生长期内会出现“ Kitamomiji 2000”，“ Super Kitamomiji”和“ Gunnison”）。结果表明，这种栽培方法使我们能够在相同的环境条件下同时生长和比较较长日和中期的栽培品种。洋葱鳞茎的发育在很长的一天中被诱导并持续存在，并且被短于一天的长度所抑制，该较短的一天中的长度长于或短于每个品种的鳞茎发育的关键日长。为了阐明这种机制，对进行了与灯泡发育有关的AcFT。我们的表达分析表明，AcFT1是根据品种的成熟程度表达的，该基因表达可作为品种成熟度和鳞茎发育的指标。结果表明洋葱对鳞茎发育的关键日长有反应，并在鳞茎比率大大超过2之前开始鳞茎发育。该指标可作为鳞茎发育的指标。