# Localized chilling of crowns promotes floral bud differentiation in strawberry transplants in a closed transplant production system

## TL;DR

Cooling strawberry plant crowns at specific times and temperatures helps promote flower bud growth in a controlled system, even under warm conditions.

## Contribution

A novel method of localized chilling for floral bud differentiation in strawberries under high-temperature conditions in a closed system.

## Key findings

- Four weeks of 10 or 15°C nighttime chilling promoted floral bud differentiation under 25/20°C air temperature and 10-hour photoperiod.
- Six weeks of 5°C daytime or entire-day chilling under 28/21°C and 14-hour photoperiod further enhanced bud differentiation.
- Plant growth was unaffected by localized chilling, showing its effectiveness without disrupting vegetative growth.

## Abstract

A stable supply of transplants with floral buds is required to improve the initial yield of the June-bearing cultivars of strawberry (Fragaria × ananassa Duch.). A closed transplant production system (CTPS) enables year-round production to meet the demands for the year-round production of strawberries in plant factories. In this study, we evaluated the performance of a novel method involving the localized chilling of strawberry crowns using silicone tubes containing circulated chilled water at different temperatures (10, 15, or 20°C) at the nighttime and different chilling regimes (daytime, nighttime, or entire day) under high air temperature conditions in a CTPS in terms of floral bud differentiation. We observed that 4 weeks of localized chilling at 10 or 15oC during the nighttime under the air temperature of 25/20°C (photo-/dark periods) and a photoperiod of 10 h promoted floral bud differentiation, whereas 6 weeks of localized chilling under the same conditions inhibited differentiation. Moreover, 4 weeks of localized chilling at 5oC during the daytime or entire day under the elevated air temperatures of 28/21°C and an extended photoperiod of 14 h promoted floral bud differentiation, and 6 weeks of localized chilling during the entire day under the same conditions further promoted bud differentiation compared with that in the control. Plant growth was generally unaffected by the localized chilling of the crowns. The results indicate that to cope with the impacts of elevated air temperature and photoperiod conditions, the continuous localized chilling of crowns at 5oC during the entire day for 6 weeks must be used to achieve optimal bud differentiation. These findings suggest the effectiveness of the localized chilling of the crowns for floral bud differentiation in strawberry in CTPSs, without disrupting the high-air temperature and long-day conditions required for vegetative growth.