An object of the present invention is to provide early and high-quality flowering and fruiting of plants, which can enhance the coloring of fruits, increase the content of essential amino acids and / or γ-aminobutyric acid (γ-ABA), or promote the coloring of harvested fruits. Provided is a safe agricultural and horticultural composition that improves the yield of a plant (fruit or cereal). An agricultural and horticultural composition comprising isoleucine as an active ingredient, which is sprayed on a vegetable, fruit tree or cereal plant or harvested fruit as a solution having an isoleucine concentration of 0.5 mM to 75 mM, comprising: At least one of promotion of flowering, promotion of fruit set, improvement of fruit set, promotion of fruit coloring, improvement of essential amino acids and / or γ-ABA content, promotion of carotenoid synthesis, and improvement of antioxidant action Play one. [Selection] Figure 2【課題】植物の開花や着果、果実の着色、必須アミノ酸及び／又はγ-アミノ酪酸（γ-ABA）含量の増加又は、収穫した果実の着色を促進することができる、早期に高品質な植物（果実又は穀物）の収穫量を向上させる安全な農園芸用組成物を提供する。【解決手段】イソロイシンを有効成分として含み、イソロイシン濃度が０．５ｍＭ～７５ｍＭの溶液として果菜、果樹若しくは穀物植物又は収穫された果実に散布される、農園芸用組成物を、植物の葉面及び／又は果実に散布して、開花促進、着果促進、着果数向上、果実の着色促進、必須アミノ酸と及び／又はγ-ABA含量向上、カロテノイド合成促進、及び、抗酸化作用向上の少なくとも一つを奏させる。【選択図】図２
