Abstract: Disclosed is a method for producing virus-free, rootstocks of hop, which comprises growing a cultured virus-free hop strain in a rooting medium thereby to make it shoot out roots therein followed by culture it in a rootstocks of hop-producing medium having a high saccharide concentration thereby to form rootstocks of hop in the medium. The virus-free, rootstocks of hop are produced under aseptic conditions and are out of the danger of their contamination with viruses, pathogenic vermian or parasites. The plants are highly safe and can be stored well. When planted, these actively shoot out roots and sprouts.

Abstract: A polysaccharide RDP substance having the ultraviolet absorption spectrum depicted in FIG. 1, the infrared absorption spectrum depicted in FIG. 2 and the .sup.13 C-NMR spectrum depicted in FIG. 3 is obtained from rice bran by extraction.