Relationship between Contents of Soluble Saccharide and Those of Starch in Squash Fruits (Cucurbita maxima) during Storage

Abstract

The supply of squash (Cucurbita maxima Duchesne ex Lam.) in Japan mostly depends on overseas imports from winter to spring. Cultivars with a high degree of storability are needed for the off-crop season in Japan. Since there has been little physiological analysis of the fruit with focus on varietal differences in storability, we analyzed the sugar metabolism of squash fruit during storage to establish selection indicators of storability. Squash cultivars with different degrees of storability were cultivated in Sapporo in 3 seasons (2016-18), and fruits were stored at 10 °C. Starch contents of ‘Hakushaku’ and ‘Oitokekuritan’, which are regarded as cultivars with superior storability, were higher than those of other cultivars. The rates of dry matter of the cultivars were ranked in the order of starch contents of the cultivars and were highly correlated with the total values of starch and soluble sugar contents. A decrease in starch content and an increase in soluble sugar content were observed in all of the cultivars except ‘Colinky’ during storage. The contents of sucrose in ‘Hakushaku’ and ‘Oitokekuritan’ rapidly increased during the fi rst 30 days of storage and became higher than those of other cultivars during storage. The contents of glucose in those two cultivars were lower than those in ‘Ebisu’ during storage. Similar results were obtained for ‘Yukigesho’, which showed a high starch content in 2018. Before storage, the glucose contents and total soluble sugar contents in ‘Hakushaku’, ‘Oitokekuritan’ and ‘Yukigesho’ were low.