Growth and propagation rate of strawberry transplants produced in a plant factory with artificial lighting as affected by separation time from stock plants

The suitable size of runner plants based on separation time from their stock plants was determined to maximize propagation rate of strawberry transplants using autotrophic transplant propagation method, a novel propagation method in a plant factory with artificial lighting for transplant production (T-PFAL). When runner tips with unfolded bracts were fixed on a growing medium to generate runner plants, the first true leaf, a runner, and roots of the runner plants appeared 6–10 days after fixing the runner tips (DAF), and their shoot and root dry weights significantly increased 6 and 10 DAF, respectively. The top/root ratio was the greatest 10 DAF. The net photosynthetic rate of runner plants 9, 11, and 13 DAF decreased after separation, while that at 15, 17, and 19 DAF did not. The runner plants separated from their stock plants 15, 20, and 25 DAF were successfully grown until 30 DAF; however, those 10 DAF was not. At 30 DAF, the root dry weight of the runner plants separated from the stock plants 15 DAF was smaller than that of the runner plants separated 20, 25, and 30 DAF, whereas the dry weights of leaves and runners were not significantly different. The use of small stock plants could reduce the required timescale from placing stock plants to produce new runner plants, but there was no significant difference in the timescales when the runner plants were separated 15 or 20 DAF due to the relatively insufficient growth of runner plants separated 15 DAF. These results indicate that runner plants separated 20 DAF, with two true leaves and a 5-mm crown diameter, would be suitable stock plants for the autotrophic transplant propagation method in a T-PFAL for strawberry propagation.