A novel plant germination inhibitor that without any hazardous effects on cultivated crop and without the danger of environmental pollution, can exert high efficacy with an extremely small dosage. There is provided a plant germination inhibitor comprising as an active ingredient a pigment produced in woody parts by fungi of the chlorosplenium aeruginosum genus or a pigment contained in cells of fungi of the chlorosplenium aeruginosum genus. Through the application of this plant germination inhibitor to a plant growth area during the germination period of the plant, the germination of the plant can be inhibited and the formation of rootstock tissue can be inhibited to thereby enable control of plant tissue formation.