Physiological changes during development and storage of fruit of buttercup squash in relation to their susceptibility to rot

Abstract

Various parameters were monitored during growth and storage of fruit of buttercup squash (Cucurbita maxima D. hybrid ‘Delica’) in an attempt to identify a physiological basis for the marked influence of maturity at harvest on the susceptibility of fruit to rot in storage. Protease inhibitor levels in the exudate from artificial wounds were consistently higher in the more resistant fruit, harvested within 14 days after completion of expansion, than in the less resistant fruit, harvested about 21 days later. Enzymes capable of cleaving the agluconic bond in the artificial substrates p-nitrophenyl-N-acetyl-β-D-glucosamide and p-nitrophenyl-β-D-N, N'- diacetylchitobiose, possibly functioning as exochitinases in vivo, were found in the juice of the fruit tissue, but not in the wound exudate. The late-harvested, less resistant fruit consistently exhibited higher levels of these activities than did the early-harvested fruit. Other distinguishing factors which were also higher in late-harvested than in early-harvested fruit, both at harvest and throughout storage, included total (free) titratable acids, tissue water potential, and total soluble solid concentration. Factors which were higher in the late- than in the early-harvested fruit when freshly harvested, but which did not continue to differ significantly during storage, included sucrose and citric acid contents, and capacity of seed to germinate.

Keywords:

• chitinase
• Cucurbita maxima D. hybrid ‘Delica’
• protease inhibitor
• squash fruit physiology
• storage rot susceptibility
• wound exudate