Effects of Raising Condition Using Cell Tray in an Unheated Plastic House of Cold Regions on the Development and Yield of Summer-cropping Japanese Bunching Onion (Allium fistulosum L.)

Abstract

In order to contribute to the development of a summer-cropping type of Japanese bunching onion (Allium fistulosum L.) suitable for early-harvesting (July) in colder regions, we investigated the effects of the seeding time (Sept. 1, Sept. 16, Oct. 1, Oct. 15, and Nov. 4), cell tray size (128- and 200-cell trays), and number of seedlings (one and two seedlings) per cell on the growth habits and yield performance of seedlings grown in an unheated plastic house. Seedlings of two cultivars were used in this experiment: ‘Hanemidori-ipponbuto’ (a late-bolting cultivar) and ‘Natsuougi-power’ (a heat-tolerant cultivar). For both cultivars, seedling development from early seedings was superior to that from later seedings (after Oct. 1), and development was also more favorable in seedlings grown in 128- than in 200-cell trays, and also when one seedling was seeded per cell compared to two seedlings per cell. The results of multivariate regression analysis indicated that the seeding time was the most influential factor for promoting seedling growth, whereas cutting the leaf blade, which inhibits seedling growth, was the second most influential factor. Therefore, leaf-pruning treatment could induce the slow growth of seedlings, even for those seeded earlier in the season. A practical evaluation with regard to early-harvesting was carried out using the following critera: the first priority, no flower bud differentiation on transplanting in the absence of leaf-pruning treatment; and the second priority, a leaf sheath diameter of more than 6 mm. As a result, five practical combinations of seeding time, cell tray size, and number of seedlings per cell were selected for ‘Hanemidori-ipponbuto’ [seeding on Oct. 1 in a 128-cell tray with two seedlings per cell (Oct. 1–128-cell tray–two seedlings), Oct. 1–200-cell tray–one seedling, Oct. 15–128-cell tray–one seedling, Oct. 15–128-cell tray–two seedlings, Oct. 15–200-cell tray–one seedling], whereas three combinations were selected for ‘Natsuougi-power’ (Oct. 15–128-cell tray–one seedling, Oct. 15–128-cell tray–two seedlings, Oct. 15–200-cell tray–one seedling). Except for one combination (Oct. 15–128-cell tray–one seedling of ‘Hanemidori-ipponbuto’), all seedlings showed a yield greater than 300 kg・a⁻¹, which was our target yield.