THE OCCURRENCE OF BITTER CUCUMBER (CUCUMIS-SATIVUS L. CV KAGAFUTOKYURI) IN RELATION TO PRUNING, FRUIT SIZE, PLANT-AGE, LEAF NITROGEN-CONTENT, AND ROOTSTOCK

Cucumber plant, 'Kagafuto' kyuri is mainly cultivated in the Utsugi di strict of Kanazawa City, Ishikawa Prefecture of Japan. The cucumbers a re harvested when they weigh about 800 g and cooked in salads or dishe s with a liquid starch dressing. The frequently bitter and unmarketabl e fruit harvested from April to May prompted this study. 1. In the sem i-forcing culture practiced in Ishikawa Pefecture, more fruits harvest ed on April 22 were bitter, especially those borne on the first latera l shoot than were those on the secondary lateral. The cucumbers on the first lateral shoot were harvested 19 days earlier than were those on the secondary lateral. 2. High occurrence of bitter fruit was observe d on the first lateral shoot whether the main shoot was kept as the le ader or pruned back to the first lateral shoot. Whether the leader was headed or not, harvesting of the first lateral shoot began 17 days ea rlier than were those on the secondary. 3. Regardless of the own-roote d plant and the grafted plant, the bitterness in the leaf intensified according to the leaf height on the plant, with the highest leaves bei ng the most bitter. 4. The bitterness was strong in young fruit, but i t decreased with age and size. 5. Shoots in which stems were longer an d leaves were heavier (bitter line) bore bitter fruits at higher frequ encies than did short shoots with smaller leaves (non-bitter line). 6. The total leaf nitrogen 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 of the latter. From these results, I postulate that in young, vigorous plants, a large amount of cucurbitacin C, the bitt er constituent, is synthesized, compared with older, less vigorous pla nts.