Differences in Leaf Chemistry and Glandular Trichome Density between Wild Southwestern American Hop (Humulus neomexicanus) and Commercial Hop Cultivars

The
female flowers (“cones”) of the hop plant (Humulus L.) produce compounds that contribute to the flavor
and other properties of beer. Hop leaves and cones produce many of
the same compounds, which also confer agronomic traits such as insect
and disease resistance. Targeted and untargeted ultraperformance liquid
chromatography-quadrupole time-of-flight–mass spectrometry
with Waters MSE technology (UPLC-QTof-MSE) metabolomics
were used to compare leaf phytochemical compositions of greenhouse-grown
southwestern American wild Humulus neomexicanus (A. Nelson and Cockerell) Rydb. against a group of commercial hop
cultivars consisting of both pure European Humulus
lupulus L. and European–North American hybrids.
Principal component analysis showed a clear distinction in chemical
profiles between the two groups. H. neomexicanus leaves had a significantly higher content of total α acids
(p = 4.4 × 10–9), total bitter
acids (p = 2.6 × 10–6), cohumulone
(p = 1.0 × 10–13), humulone
+ adhumulone (p = 9.1 × 10–4), and the prenylflavonoids xanthohumol (p = 0.013)
and desmethylxanthohumol (p = 0.029) as well as significantly
higher densities of glandular trichomes (p = 1.3
× 10–6), the biosynthetic site of those compounds.
Most flavonol glycosides measured were also significantly more abundant
in H. neomexicanus (p = 1.5 × 10–22 to 0.0027), whereas phenolic
acids were consistently, but generally nonsignificantly (p > 0.05), more abundant in the cultivars. The higher bitter acid,
prenylflavonoid, and flavonol glycoside content of H. neomexicanus leaves may help to confer more favorable
insect and disease-resistance properties.