Photosynthetic activity of six hop (Humulus lupulus L.) cultivars under different temperature treatments

Authors: Eriksen, Renee; RUTTO, LABAN - Virginia State University; Dombrowski, James; Henning, John

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2019
Publication Date: 4/11/2020
Citation: Eriksen, R.L., Rutto, L.K., Dombrowski, J.E., Henning, J.A. 2020. Photosynthetic activity of six hop (Humulus lupulus L.) cultivars under different temperature treatments. HortScience. 55(4):403-409. https://doi.org/10.21273/HORTSCI14580-19.
DOI: https://doi.org/10.21273/HORTSCI14580-19

Interpretive Summary: The Pacific Northwest grows the majority of the hops in the United States, however the region is experiencing an increase in the number of days with high heat. In addition, there is an increased interest in growing hops in other regions of the United States where the climate is not ideally suited for for hop growth. In order to understand how hop plants respond to high temperatures, we measured a number of physiological traits in six hop cultivars under a range of temperatures from 15 – 45°C, and we found that hop plants achieved maximal photosynthesis at temperatures of 21 – 39°C when given sufficient water. At higher temperatures, all cultivars that we tested experienced declines in photosynthesis. This is likely due to multiple effects on the cell, which we measured as damage to the light-harvesting components of the plant cells, damage to the cell membrane and declines in protein activity responsible for sugar construction. The cultivars 'Cascade', 'Southern Brewer', and 'Willamette may be good candidates for growing in warm regions because they appeared to suffer the least amount of irreparable damage due to heat. The cultivar 'Chinook' appears to be very susceptible to heat stress; we measured irreparable damage to the light-harvesting components of the plant cell and to the cell membrane integrity.

Technical Abstract: The Pacific Northwest grows the majority of the hops in the United States, however the region is experiencing an increase in the number of days with high heat. In addition, there is an increased interest in growing hops in other regions of the United States where the climate is not ideally suited for for hop growth. In order to understand how hop plants respond to high temperatures, we measured a number of physiological traits in six hop cultivars under a range of temperatures from 15 – 45°C, and we found that hop plants achieved maximal carbon assimilation at temperatures of 21 – 39°C when given sufficient water. At temperatures of 41°C and higher, all cultivars experienced declines in carbon assimilation. This is likely due to multiple effects on the cell, including damage to PSII as reflected in declines in FV/FM, damage to membrane integrity as reflected in electrolyte leakage at high temperatures, and declines in Rubisco activity due to degradation of Rubisco activase as reflected in declines in Vc,max. Cascade, Willamette, and Southern Brewer may be good candidates for growth in warm climates, since all experience relatively high rates of carbon assimilation at high temperatures, and did not experience significant declines in FV/FM or increases in electrolyte leakage. Chinook appears particularly susceptible to heat stress, experiencing evidence of irreparable damage to PSII and membrane integrity.