The hop (Humulus lupulus L.) is a dioecious, diploid (2n=2x=20) species. Triploid
hops (2n=3x=30) are easily obtained from tetraploid by diploid crosses and are preferred
because of their natural seedlessness and increased vigor. The female inflorescence is used
for flavoring beer. Because brewers require product consistency, the brewing characteristics
of a new aroma-type hop must closely match the variety it is intended to replace while
showing improved adaptation and agronomic traits. Since triploid offspring should more
closely resemble the tetraploid parent from which they receive two-thirds of their genetic
material, breeders have traditionally selected known varieties to be the tetraploid parent with
the expectation this will increase the likelihood of obtaining progeny with similar brewing
chemistry. Tetraploid female parents are obtained through colchicine treatment of desirable
diploid varieties.
Naturally occurring tetraploid seedlings, sometimes found among the offspring of
tetraploid by diploid crosses, if suitable for breeding, could eliminate the tedious colchicine
treatment process now used to obtain tetraploids. Two such tetraploid males were obtained
from an Oregon cross in 1983. Since these two tetraploid males had attractive quality traits
similar to other males in the USDA germplasm collection with a proven history of producing
aroma-type progeny, they were thought to be suitable for use in a polyploid breeding program
for aroma hops.
The objective of this study was to determine the feasibility of using males as tetraploid
parents in diploid by tetraploid crosses to obtain triploid aroma hops. Tettnanger, a prized
German aroma hop, was used as the diploid female parent for these crosses.
Meiotic cells of the two tetraploid males showed some abnormalities at anaphase I and
the quartet stage; however, fertility, as determined from seed production and germination,
was adequate for breeding. Of 185 seedlings obtained, 57 were triploid females. The diploid
by tetraploid seedling population had a higher percentage of males than previously reported
for tetraploid by diploid crosses. One tetraploid male produced no triploid female offspring.
Seed content of the female triploid seedlings when subjected to a heavy pollen load averaged
2.4% compared to 20.1% for diploid seedlings from Tettnanger crosses. Triploid progeny
produced higher average yield than the Tettnanger parent.
The two tetraploid males and Tettnanger were very similar in chemical quality traits
comparable in male and female hops. Comparison among triploid and diploid progeny from
diploid by tetraploid crosses and diploid open-pollinated Tettnanger seedlings demonstrated
that the male parent influenced the a ratio, cohumulone content, and humulene to
caryophyllene ratio of the offspring. Many of the female triploid offspring genotypes showed
chemical quality traits similar to those of Tettnanger. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35084 |
| Date | 04 November 1994 |
| Creators | DeNoma, Jeanine Streeter |
| Contributors | Haunold, Alfred |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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