Determining grafting compatibility for some selected intraspecific pumpkin as rootstock (Cucurbita moschata) with watermelon (Citrullus lanatus)

The mechanism of graft compatibility between pumpkin rootstocks and watermelon remains unclear, leading to the absence of scientifically validated physiological and biochemical criteria for selecting elite rootstocks. To evaluate graft compatibility and characterize associated morphological and physiological responses, four pumpkin hybrid combinations conferring dual resistance to Fusarium wilt and root-knot nematodes were employed as rootstocks for grafting onto representative large-fruit and small-fruit watermelon cultivars, with non-grafted seedlings used as the control. The results showed that after grafting with large-fruited watermelon, multiple root system morphology indicators (root length, root projection area, root surface area and lateral root number) and POD enzyme activity were significantly higher than those of non-grafted seedlings. Among them, the hybrid combination Renhe-1×Lingchuan C1 exhibited the highest SOD enzyme activity, reaching 234.75 U/g. After grafting with small-fruited watermelon, multiple root system morphology indicators (root length, root projection area, root surface area, root volume, root tip number and lateral root number) and root system vitality were significantly higher than those of non-grafted seedlings. Among them, the hybrid combination Renhe-1×Daziwang-24 exhibited the highest root system vitality, reaching 2.51 mg·g − 1 ·h − 1 ; its MDA content was significantly lower than that of non-grafted seedlings. The results demonstrate that Renhe-1 × Lingchuan C1 and Renhe-1 × Daziwang-24 are the top-performing rootstock combinations for both large-fruited and small-fruited watermelon scions.