LAUSR

Abstract Atlantic Giant (AG), the world largest pumpkin, was bred through continuously crosses and strict selections from the small fruit ancestor. To understand the change caused by the artificial cross and selection in the recent 100 years, differences of morphology, anatomy and physiology between two cultivars with distinct fruit size in Cucurbita maxima, AG and Hubbard were investigated. Comparing with Hubbard, AG owns more fruit cell number and larger fruit cell volume at harvest stage, accompanied by larger leaves, higher net photosynthetic rate, lower leaf total sugar concentration, higher leaf stachyose level, larger peduncle vascular cross area and higher phloem sap sugar concentration. Further theoretical calculation indicates that AG needs more leaves and longer translocation time per day to support its huge fruit growth. In addition, considerable glucose and stachyose were found in the phloem sap and sarcocarp of AG respectively, suggesting different loading and unloading mechanisms are involved in the giant pumpkin growth. These results provide useful cues for improving cultivation and breeding techniques of giant pumpkins.