A composition for agricultural or horticultural application, which contains isoleucine as an active ingredient, and is sprinkled on a fruit vegetable, fruit tree, or grain plant, or a harvested fruit as a solution having an isoleucine concentration of 0.5 to 75 mM, is sprinkled on a leaf surface and/or a fruit of a plant to provide at least one of promotion of blooming, promotion of the appearance of the fruit, improvement in number of fruit produced, promotion of coloring of fruit, improvement in essential amino acid and/or ³-ABA content, promotion of carotenoid synthesis, and improvement in antioxidant capacity.
