*3.1. Graft Survival Rate*

In the 2016 pilot study, the survival rate of MQ/BK was 95.8% at 13 DAG but decreased to 87.5% at 68 DAG (data not shown). In the 2019 experiment, there was no difference in survival rate (*p* = 0.483) between BK/BK (79%), MQ/MQ (92%), and MQ/BK (77%) at 17 DAG (data not shown). The relatively high survival rates of MQ/BK indicated good graft compatibility between 'Mei Qing Choi' pac choi and 'Bora King' daikon radish. Both the edible pac choi leafy green part of the plant and the radish taproot developed in MQ/BK (Figure 1A–C). According to Oda and Nakajima [8], 'Taibyoh 60-nichi' Chinese cabbage grafted onto 'Taibyoh hikari' turnip had a survival rate of only approximately 50%; however, it was attributed to the small size of the seedlings at grafting rather than graft incompatibility. In our studies, we also used 1.5 mm or even smaller grafting clips to graft younger and tender seedlings as the hypocotyl tissue of radish and pac choi plants tend to become more lignified as they grow. The lower survival rate observed in the 2019 experiment may have been due to an issue with properly matching the plant stem diameters at grafting since the hypocotyl of the daikon radish plant had grown thicker than expected at the time of grafting. As stem diameter and alignment of cambial tissues affect the success of grafting [18–20], matching plant stem diameters between these two species, which have thin hypocotyls at the optimum stage for grafting, is a challenge for achieving successful grafts. In this study, daikon radish was seeded 6 d earlier than pac choi to help match their stem diameters, but with less than desirable results, especially in the 2019 experiment owing to the seasonal variability of greenhouse conditions that led to unpredictable growth rate of plants. As shown by Hayashida et al. [21] and Kwack et al. [22], the hypocotyl growth of pac choi and radish seedlings can be manipulated by light quality and intensity. Employing a more controlled environment for growing seedlings until ready for grafting seems to be advisable for future work.

$$\mathbf{(A)}\tag{B}$$

(**C**) (**D**)

(**E**) (**F**)

**Figure 1.** *Cont.*

(**G**)

**Figure 1.** Grafted plants with 'Mei Qing Choi' pac choi as scion and 'Bora King' daikon radish as rootstock. (**A**) A well-healed grafted pac choi–daikon radish seedling. (**B**) Formation of the taproot of daikon radish grafted with pac choi. (**C**) Longitudinal section of the grafted pac choi–daikon radish plant at harvest. (**D**) Comparison between self-grafted 'Bora King' (left), 'Mei Qing Choi' pac choi grafted onto 'Bora King' daikon radish (middle), and non-grafted 'Bora King' (right) at harvest. (**E**) Longitudinal section of the graft union area of grafted pac choi–daikon radish plant at harvest. (**F**) Longitudinal section of the graft union area of self-grafted 'Bora King' daikon radish at harvest. (**G**) Longitudinal section of the graft union area of self-grafted 'Mei Qing Choi' pac choi plant at harvest.
