The occurrence of bitter cucumber (Cucumis sativus L. cv. Kagafutokyuri) in relation to pruning, fruit size, plant age, leaf nitrogen content, and rootstock.

摘要

Kagafutokyuri cucumbers cultivated in the Utsugi district of Kanazawa City, Ishikawa Prefecture, Japan are frequently bitter and unmarketable when harvested from April to May. In trials using the the semiforcing culture practiced in Ishikawa Prefecture, many fruits harvested on 22 April were bitter, especially those borne on the first lateral shoot rather than the secondary lateral. The cucumbers on the first lateral shoot were harvested earlier than were those on the secondary lateral. A high occurrence of bitter fruits was observed on the first lateral shoot whether the main shoot was kept as the leader or pruned back to the first lateral shoot. Regardless of whether plants were own-rooted or grafted, leaf bitterness intensified with increasingleaf height on the plant. Bitterness was strongest in young fruits, decreasing with age and size. Shoots in which stems were longer and leaves were heavier (bitter line) bore bitter fruits at higher frequencies than did short shoots with smaller leaves (non-bitter line). The total leaf N content of the bitter line was equal to that of the non-bitter line but the leaf nitrate ion content of the former was less than half that of the latter. From these results it is postulated that more cucurbitacin C, thebitter constituent, is synthesized in young, vigorous plants, than in older, less vigorous plants.