As the adoption of grafting technology is increasing among growers to manage soilborne diseases in watermelon production and new rootstocks are being developed, more research is needed to test different combinations of rootstocks and scions to identify growth differences that may be influenced by rootstock-scion interactions. In this greenhouse pot study, we examined the impact of the interspecific hybrid squash rootstock ‘Camelforce’ (Cucurbita maxima × C. moschata) and the wild watermelon rootstock ‘Carolina Strongback’ (Citrullus amarus) on the growth and development performance of two seedless watermelon scion cultivars with contrasting fruit maturity characteristics. Two weeks after seeding, early-maturing ‘Citation’ and late-maturing ‘Miramonte’ seedless watermelon plants were grafted onto each rootstock, respectively, with non-grafted scions and rootstocks as controls. The plants were arranged in a randomized complete block design with five replications and three plants per experimental unit. Non-grafted ‘Camelforce’ showed the longest primary vine, while ‘Miramonte’/‘Camelforce’ displayed significantly higher total vine length than other treatments. Non-grafted ‘Carolina Strongback’ exhibited significantly more leaves, followed by ‘Miramonte’/‘Camelforce’ and non-grafted ‘Miramonte’. ‘Camelforce’ also exhibited significantly greater above and below-ground dry weights, followed by ‘Miramonte’/‘Camel force’, although it did not differ from non-grafted ‘Miramonte’. The dry weights of ‘Citation’/‘Camelforce’ were significantly higher than non-grafted ‘Citation’. The above-ground dry weight of ‘Citation’/‘Carolina Strongback’ was significantly lower than all groups, except for non-grafted ‘Carolina Strongback’. Similarly, the below-ground dry weight of ‘Citation’/‘Carolina Strongback’ was significantly lower than treatments, except for ‘Miramonte’/‘Carolina Strongback’ and non-grafted ‘Carolina Strongback’. All treatments showed male and female flowers by week 3 after transplanting. Both non-grafted rootstocks showed more female flowers than non-grafted and grafted scions. At week 4 ‘Miramonte’/‘Carolina Strongback’ had more female flowers than all other treatments, while non-grafted ‘Camelforce’ exhibited the lowest. No difference in female flowers between the grafted and non-grafted scion groups was observed. Non-grafted scions exhibited more male flowers than the respective grafted plants by week 3. No differences were observed in male flowers except ‘Citation’/‘Carolina Strongback’ with fewer than grafted and non-grafted scions by week 4. Week 3 female flowers results suggest that grafting can significantly affect plant growth, but has a limited impact on flowering. The ‘Miramonte’/ ‘Camelforce’ group exhibited vigorous growth without significantly affecting flowering. Further research is necessary to explore how different types of rootstocks may impact fruit development of watermelon scions of varying fruit development characteristics in commercial production.
