Minimum Leaf Age Required for Flower Bud Induction in the Seed-propagated Strawberry Cultivar ‘Yotsuboshi’ under a Closed Plant Production System

Abstract

　The recent rise in temperatures has delayed strawberry flower bud differentiation and reduced the flowering ratio. To achieve a sufficient flowering ratio, we used a closed plant production system (CPPS) to induce flower buds in a seed-propagated cultivar ‘Yotsuboshi,’ which is not influenced by any prior cultivation history inherent to vegetative propagation. Due to the tier height constraints of CPPS, we determined the minimum leaf age―the number of leaves that emerged from sowing―under short-day and night-chilling treatments for 21 days, at which a sufficient flowering ratio was achieved. The leaf age of seedlings at the beginning of treatments was limited to a maximum of 4. Even when transplanted during summer, the application to leaf age 3 and 4 seedlings reached flowering ratios of 90% and 80%, respectively. In winter, leaf age 3 and 4 seedlings also attained a 100% flowering ratio. The period from greenhouse transplantation to flowering was evaluated at comparable values using the effective cumulative temperature with a base temperature of 7℃ during both summer and winter. Furthermore, we confirmed that leaf age 4 seedlings reached flowering at a similar effective cumulative temperature under forcing culture conditions, followed by fruit set and harvest.