Inhibition of flowering of cucumber grafted on rooted squash stock

For the elucidation of the mechanisms of floral transition in indifferent plants, cucumber seedlings (Cucumis sativus cv. Rennsei or cv. Shimoshirazu‐jibai) were grafted onto squash seedlings (Cucurbita maxima Duchesne X C. moschata Duchesne cv. Shintosa‐ichigou) of which the meristems had been removed, and the effect on flower induction on the cucumber scion was examined. In both cultivars, the grafted cucumber bore no flowers, whereas control plants developed flowers above the second to fourth nodes. The inhibition of flower formation on the grafted cucumber scion occurred even when the root of cucumber was left with the squash root on the grafted plant, and flower formation occurred after removal of the squash stock. The inhibitory effect of the squash stock in the presence of the cucumber root was abolished by removal of the squash root. Neither the dry weight of stem plus leaf nor the chlorophyll content of the leaf, as indicators of vegetative growth, were correlated with flower formation on cucumber plants that had been grafted in the presence of cucumber roots on whole, cotyledon‐free or root‐free squash stock. These results indicate that flower formation in cucumber was inhibited by a factor produced by squash roots, an inhibition probably not involved in the modulation of vegetative growth. The root may control floral transition by the production of inhibitory factors in some day‐neutral Cucurbitaceae plants.