PURPOSE:To provide the subject agent composed of a filtrate of the culture product of a photosynthetic procaryotic microorganism or its extract and capable of efficiently performing the growth of an adventitious embryo and, accordingly, effective in improving the efficiency of a mass-breeding process of clone plant comprising the regeneration of a plant body via an adventitious embryo. CONSTITUTION:An adventitious embryo induced from a plant tissue or a vegetative cell by a plant tissue culture technique is grown by using a filtrate of the culture product of a photosynthetic procaryotic microorganism or its extract as an agent for promoting the growth of adventitious embryo. The photosynthetic procaryotic microorganism is e.g., Chlorogloeopisis sp. ATC 27181. The above growth-promotion agent is used by adding to a basal medium.
