A composition for agricultural and horticultural use, which contains isoleucine as an active ingredient and is applied to fruit vegetables, fruit trees or cereal plants or harvested fruits as a solution having an isoleucine concentration of 0.5 mM to 75 mM, on the leaves and / or fruits of the plant. Sprinkling to promote at least one of flowering promotion, fruit setting promotion, fruit number improvement, fruit coloring promotion, essential amino acid and / or γ-ABA content improvement, carotenoid synthesis promotion, and antioxidant action improvement .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。
