トマト栽培において，シンクソースの割合の変動は，物質生産において大きな影響をもたらすとされる．生産性向上や栄養成長と生殖成長のバランスを保つための手段として摘葉が行われている．本研究では，未熟葉の摘葉が物質生産に及ぼす影響を調べるために，日本およびオランダの4 品種を用い，15 週間ハイワイヤー誘引による多段栽培を行った．摘葉処理として果房間に着生する3 枚の葉から，果房直上の1 枚を，まだ展開していない未熟な状態で定期的に除去しながら栽培し，群落内の光環境，生育および収量に及ぼす影響について調査した．いずれの品種でも，未熟葉の除去によって，着生葉数は減少するが，平均個葉面積は大きくなり，節間長は短くなった．また，摘葉処理により，積算受光量，光利用効率に影響を及ぼしたが，その反応は品種によって異なった．総乾物生産量については，いずれの品種でも摘葉処理による有意な差はなかったが，未熟葉の除去は地上部の乾物分配に影響し，摘葉処理区では茎葉の乾物分配率が減少すると共に，果実への分配率が増え，いずれの品種も，摘葉処理区の収量が増加した．本研究では，果実への乾物分配および収量などの結果から，果房直上の未熟葉の摘葉は，トマトの収量向上を可能にすることを示した．In tomato plants, fluctuation of sink–source ratio greatly influences the productivity. Defoliation is used as a means to improve yield and maintain a balance between vegetative and reproductive growths in tomato cultivation. Experiments were performed to investigate the influence of defoliation of immature leaves on growth and yield, by assessing the change in light use in the canopy and measuring the yield and yield components. Four different tomato cultivars of Japan and the Netherlands were grown hydroponically with a high-wire system in a greenhouse for 15 weeks. As a defoliation treatment, one out of every three leaves occurring between trusses was removed periodically. Only immature leaves of length 5 cm or less were removed. Although the number of leaves attached to the stem during the cultivation period decreased in all cultivars because of defoliation, the individual leaf area increased, and the internode length decreased. In addition, the cumulative intercepted light and light use efficiency were affected by defoliation, but the results varied depending on the cultivar. No significant difference was noted in the total dry matter production with defoliation, regardless of the cultivar. However, removal of the immature leaves markedly affected the distribution of dry matter. The defoliated tomato plants showed decreased stem and leaf dry matter ratio, but increased fruit dry matter ratio, regardless of the cultivar. The defoliation treatment also increased the yield of the tomato plants.It is concluded, based on fruit dry matter distribution and yield components data, that the removal of one immature leaf between trusses would improve tomato yield.