Effects of Grafting Methods and Re-rooting on the Growth Characteristics of Grafted Muskmelon Plants

Grafting has been used as an effective approach to controlling soil-borne diseases and overcoming abiotic stresses in production of solanaceous and cucurbitaceous vegetables. With respect to melon grafting, grafting methods vary considerably among geographic regions and nurseries, while the practice of rootstock re-rooting during graft healing process has been used by some propagators. In this study, three grafting methods including hole-insertion (HI), one-cotyledon (OC), and non-cotyledon (NC) methods were examined for their influences on the seedling growth and root characteristics of muskmelon ‘Athena’ (Cucumis melo) grafted onto hybrid squash rootstock ‘Strong Tosa’ (Cucurbita maxima × Cucurbita moschata). Non-grafted rootstock and scion plants were included as controls. Both grafted and non-grafted plants were examined with or without re-rooting. Root measurements were conducted every four days after grafting (DAG). At 16 DAG, root length and surface area and average root diameter were similar between re-rooted plants and plants without re-rooting (with original roots). NC method resulted in a decrease in root length and surface area as well as shoot fresh and dry weights compared with HI and OC methods and non-grafted controls. Due to the reduced transplant quality, NC method was excluded from the following experiment. In the second part of the experiment, plants were transplanted into 3.8 L pots and grown in a greenhouse until anthesis of melon female flowers, and belowground and aboveground growth characteristics were then evaluated. Flowering time did not differ between HI- and OC-grafted plants and non-grafted scion controls. Shoot fresh and dry weights, leaf area, chlorophyll content, and stomatal conductance were also similar between these treatments. Re-rooting did not impact aboveground growth characteristics. Interestingly, the re-rooted rootstock controls generated longer roots compared with those without re-rooting; however, this was not observed on grafted plants and non-grafted scion controls. The experiment demonstrated that NC method suppressed root development and reduced transplant quality. HI and OC methods did not show any significant effects on aboveground and belowground growth characteristics compared with non-grafted scion and rootstock controls, respectively. Further studies are warranted to evaluate the field performance of re-rooted grafted melon plants.