Application of newly-developed tools for high throughput analysis to assess the effects of prohexadione-Ca on the phytochemical, morphological, and targeted metabolic profile of hops (Humulus lupulus)
Kavalier AR., Yang H., Kennelly EJ., Coles MC., Dinh T., Koelling J., Matthews PD.
Hops (Humulus lupulus L.) is a medicinal plant that is also used in the brewing of beer for flavor, stability, and process. Economically valued secondary metabolites produced in floral organs and especially in trichomatous glands of cones are the focus of breeding and metabolic engineering. To facilitate these efforts several phenotyping methods were developed for hops, including (1) high throughput digital-morphometrics, (2) ultra high performance liquid chromatography, and (3) capillary liquid chromatography coupled to positive-mode electrospray ionization quadrapole time-of-flight mass spectrometry (capLC-ESI-QToF-MS). These methods were demonstrated by application to morphological and metabolic changes occurring upon treatment of hops with prohexidione-calcium (Pro-Ca). Hop plants of two varieties, 'Willamette' and 'Zeus', were treated with Pro-Ca at a range of dosage levels (50-450 ppm) and treatment time-points (early-, middle-, and late-stages of flowering) to determine the most effective parameters for Pro-Ca application to hops. Data were analyzed by one-way ANOVA, which revealed significant differences between control and treated samples. When hop plants were treated with low doses of Pro-Ca during late-stages of flowering we detected agronomically-positive effects, namely: (1) a 14.6% increase in cone yield (kgs/hectare) in 'Willamette' (p=0.025), and (2) a 30-48% increase in desmethylxanthohumol, xanthohumol, humulones, and lupulones in 'Zeus' (p<0.001). Preliminary metabolic profiling of treated 'Willamette' hop cones by capLC-ESI-QToF-MS evidenced many metabolic changes that suggest Pro-Ca inhibition of hop FHT.