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Hop Yield Stimulation by Triploid Males Under Field Conditions¹

Triploid male hops (Humulus lupulus L.) have the potential for yield stimulation of diploid female cultivars without excessive production of unwanted seeds, as shown from earlier hand-pollination experiments during the 1972 and 1973 growing seasons. However, confirmatinn of these data from commercial field testing of triploid pollinators was still needed before specific pollinators could be recommended to growers.

Twelve triploid male hop genotypes were field-tested or cone yield stimulation in a commercial seedless-hop production area. Cone yields of a 6.8 ha field of ‘Brewer's Gold,’ a diploid cultivar, pollinated by triploid males averaged 30% higher than those of an untreated 12 ha control field nearby. The -acid content in the cones from the two fields did not differ significantly. However, production of -acid, which is the desired product, was substantially higher for the field pollinated by triploid males due to higher cone yields. Seed-set due to triploid males averaged 4% compared to the 2% background seed-set of the control. Females in the immediate vicinity of triploid pollinators showed substantial cone-size and weight stimulation. There were significant differences in seed production of Brewer's Gold plants fertilized by different triploid pollinators, reflecting variation in synchronization of flowering with Brewer's Gold, as well as differences in amount of pollen production among males. Seeds from the triploid-pollination treatment averaged about half the weight of seeds from the control yard. In another experiment, seeds from hand-pollination of diploids with triploid males contained about 25% fewer lipids and 14% less crude protein than those from pollination by diploid males involving the same female test plant.

Commercial use of triploid pollinators in seedless-hop production areas would probably result in a seed content of 2 to 3% and a cone-yield increase of 15 to 25%, accompanied by a corresponding increase in -acid production per ha. Eight triploid males were identified as suitable Brewer's Gold pollinators under Oregon conditions.

Key Words: Pollination • Cone weight • Seed set • Seed weight • Seed lipids • -acid • ß-acid • Humulus lupulus L.

² Research geneticist, USDA-SEA-AR, Dep. of Crop Science; and chemist, Dep. of Agricultural Chemistry, Oregon State Univ., Corvallis, OR 97331.

Received for publication July 17, 1978.