A Comparative Study on the Growth and Bulb Development of Several Onion (Allium cepa L.) Cultivars Sown in Spring in the Northeast Region of Japan

抄録

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.