Comparative analysis of assimilate synthesis, translocation and partitioning between two Cucurbita maxima cultivars “Atlantic giant” and “Hubbard”

•Comparing Hubbard.•AG owns larger leaf area, higher net photosynthetic rate and leaf stachyose level.•AG has larger phloem cross area and higher sugar concentration in phloem sap.•AG unloads stachyose directly into fruit without catabolism at fast growing stage.