The present invention provides: a method for producing stolon-forming plant having an improved tuber production ability as compared with a corresponding wild strain and a stolon-forming plant produced by the method. The present invention also provides: a method for producing a stolon-forming plant having an improved stolon formation ability as compared with a corresponding wild strain a stolon-forming plant produced by the method and a kit for improving a stolon formation ability of a stolon-forming plant. The method of the present invention is a method for producing a stolon-forming plant having an improved tuber production ability as compared with a corresponding wild strain, the method including the step of introducing, into a stolon-forming plant, a Ran gene derived from Citrullus lanatus. The method of the present invention can further include the step of introducing, into a stolon-forming plant, a polynucleotide encoding fructose-1,6-bisphosphatase/sedoheptulose-1,7-bisphosphatase derived from a blue-green alga.
