Fuente: WIPO "tomato" A plant growth promoter, including: a lignin sulfonic acid component, where a phenolic hydroxyl group content of the lignin sulfonic acid component is 0.1% to 3.5% by weight, a methoxyl group content of the lignin sulfonic acid component is 1.0% to 15.0% by weight, and a sulfone group-derived sulfur atom content of the lignin sulfonic acid component is 2.0% by weight or higher. A biostimulant, including: a lignin sulfonic acid component, where a phenolic hydroxyl group content of the lignin sulfonic acid component is 0.1% to 3.5% by weight, a methoxyl group content of the lignin sulfonic acid component is 1.0% to 15.0% by weight, and a sulfone group-derived sulfur atom content of the lignin sulfonic acid component is 2.0% by weight or higher.