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Use of Triploid Males for Increasing Hop Yields¹

Hand pollination of receptive flowers of six diploid cultivars of hop (Humulus lupulus L.) increased cone size by 7 to 24%, regardless of ploidy level of the pollen parent. In 1973, cone weights, which directly affect yield, increased an average of 46% when female flowers had been pollinated from diploid males and 17% upon pollination from triploid males. Bracts plus bracteoles increased an average of 23% over the untreated control from the diploid pollination treatment, and 11% from the triploid pollination treatment. Pollination had the most striking effect on strig length and strig weight, but little effect on number of nodes/strig. Seeds from the triploid pollination treatment averaged less than half the weight of the open-pollinated control and contained 60 to 83% aborted embryos, whereas seeds from the diploid pollination treatment contained only 18%. Well-filled seeds were purple, and usually weighed three to four times as much as tan seeds. Seeds resulting from the triploid pollination treatment had about 25% less crude fat than seeds of the control.

Hop yields in seedless production areas probably can be increased significantly without additional production costs (except for harvesting a larger crop) by use of pollen from triploid males to stimulate cone size and weight. Such cones look like seeded cones, but contain only about one-fourth as many seeds as those pollinated by comparable diploid males. They will probably mature earlier and tend to shatter, as do seeded cones. Replacing diploid by triploid males in presently seeded hop yards will probably decrease yields slightly from lack of seeds. This decrease will probably be offset by the premium received for a seedless crop.

Key Words: Pollination • Yield stimulation • Seed set • Seed color • Seed weight • Aborted embryo • Cone size

² Research geneticist, ARS-USDA, Dep. of Agronomic Crop Science, Oregon State Univ., Corvallis, OR 97331.

Received for publication April 21, 1975.