*2.2. Setup of the Follow-Up Experiment*

A follow-up experiment was conducted in 2019 to further explore the above-ground growth and below-ground taproot development in grafted pac choi–daikon radish plants. 'Mei Qing Choi' (MQ) pac choi was grafted onto 'Bora King' (BK) daikon radish (MQ/BK), while non-grafted pac choi (MQ) and daikon radish (BK) as well as self-grafted pac choi (MQ/MQ) and daikon radish (BK/BK) were used as controls. A randomized complete block design with four replications (blocks) and ten grafted plants per treatment per replication (block) was used in the grafting experiment. MQ and BK were seeded into 72-cell trays on 8 and 14 February 2019, respectively. Fish & seaweed organic liquid fertilizer 2N-1.3P-0.8K (Neptune's Harvest, Gloucester, MA, USA) and 0N-0P-41.5K potassium sulfate (Big K; JHBiotech, Inc., Ventura, CA, USA) were applied at concentrations of 200 mg L−<sup>1</sup> N and 200 mg L−<sup>1</sup> K2O at the seedling growth stage on 18 and 26 Feb. Plants were grafted on 1 March 2019 using the aforementioned grafting method. Grafted plants were healed in an air-conditioned laboratory room with the same set up of healing chamber as in 2016. Supplemental light was provided for 10 h each

day during the healing process. The air temperature and RH of the laboratory room were 23.8 ± 0.5 ◦C and 47.6 ± 13.1%. The plastic film was completely removed at 8 DAG. Water was gently sprayed onto the soil surface using a wash bottle when needed to avoid wetting foliage. All the grafted plants were moved into a greenhouse at 13 DAG where the average day and night temperatures were 27.1 ◦C and 20.7 ◦C, respectively. Graft survival rate was determined for each grafting treatment in each replication by counting the number of live and dead plants at 17 DAG. At 19 DAG, 24 plants from each treatment with healthy and consistent growth were chosen and randomly reassigned to four blocks with six plants in each block for further evaluation of the growth of the grafted plants in a greenhouse pot study, following a randomized complete block design. Plants were transplanted into 11.36 L black plastic pots filled with PRO-MIX premium organic vegetable and herb mix (Premier Tech Ltd., Quakertown, PA, USA) which contained 60–75% peat moss plus peat humus, compost, perlite, gypsum, limestone, organic fertilizer, and mycorrhizae. Drip irrigation was used by placing one 1.89 L h−<sup>1</sup> emitter in each pot; the plants were watered twice a day for 3 min per cycle between 21 and 39 DAG and irrigation increased to 4 min per cycle thereafter. Adventitious roots developed from the graft union area were monitored and removed once a week as needed after the plants were transplanted into the pots.
