Comprehensive Mineral Nutrition Analysis of Watermelon Grafted onto Two Different Rootstocks

Grafting is a widely used practice in fruit-bearing vegetables. However, why grafting affects plant growth, fruit yield, and quality, especially from the aspect of mineral nutrition, remains unclear. In this study, watermelon cultivar ‘Zaojia 8424’ was grafted onto bottle gourd ‘Jingxinzhen 1’ (Lagenaria siceraria) and pumpkin ‘Qingyanzhen 1’ (Cucurbita maxima × C. moschata). Non-grafted plants were used as the control. Results show that rootstock grafting significantly increases plant growth and single fruit weight of watermelon. Watermelon grafted onto rootstocks, especially pumpkin, exhibits significantly higher root volume, root surface area, and number of root tips and forks in comparison with non-grafted plants. Fruit flesh, rind firmness, and rind thickness were enhanced by grafting. However, fruit soluble solids and taste significantly decreased in plants grafted onto pumpkin. The total uptake (mg ⋅ plant−1) and concentration (mg ⋅ g−1 DW) of N, K, Ca, Fe, Mg, and Mn in root, stem, leaf, fruit rind, and flesh were generally higher in grafted plants compared to non-grafted ones, especially for N of pumpkin rootstock-grafted plants. The total uptake of nutrients of plants grafted onto bottle gourd and pumpkin was increased by 30.41% and 49.14% at fruit development stage and by 21.33% and 47.46% at fruit maturation stage, respectively, compared with non-grafted plants. We concluded that watermelon grafting onto suitable rootstocks can increase the uptake of mineral nutrition, especially for N in the pumpkin rootstock grafted plants, thereby affecting plant growth, fruit yield, and quality.