A shoot-tip culture procedure has been developed to eliminate the five hop viruses known to occur in the U.S. Hop shoot-tips 0.5 mm long are grown to full height in a liquid culture medium. When a single virus free plant has been obtained, several hundred thousand identical virus free plants can be produced by soft-wood propagation in the greenhouse and transplanted in the hop yards. Virus free rootstock has been produced for each of the major hop varieties grown in the U.S. and most of these have been established in large acreages. Over 800,000 virus-free plants have been replanted on nearly 1,000 acres of the John I. Haas Inc. hop farms over the last three years. These new rootstocks are more vigorous, mature earlier, develop greater side-arm growth, have increased cone yield and alpha-acids content and are free of the virus induced symptoms of the standard rootstocks.
Keywords : culture hops removal virus