S.T. Kenny
The purpose of this study was to determine the effect of light intensity, leaf position, leaf development and genotype on hop (Humulus lupulus L.) photosynthetic rate, as measured by net assimilation of CO2, A, and stomatal conductance to water vapor (gs) using field measurements of single hop leaves. Light saturation of photosynthetic activity in ‘Willamette’ occurred near a maximum photon flux density (PFD) of 2000 μm m-2 s-1 while light saturation in ‘Galena’ occurred near a PFD of 1800 μm m-2 s-1. The photosynthetic rate of ‘Galena’ leaves in any sunlit portion of the canopy averaged 16.6 μmol CO2 m-2 s-1 while shaded leaves throughout the canopy had negligible photosynthetic activity. Sunlit leaves averaged 60% higher stomatal conductance than the shaded leaves. Leaves at 75% or greater expansion had the highest photosynthetic rate. The average photosynthetic rate of 40 genotypes, including cultivars, native North American and native Yugoslavian germplasm, and breeding lines, was 16.2 μmol CO2 m-2 s-1. The range in photosynthetic rate was between 9.0 and 22.3 μmol CO2 m-2 s-1. The average stomatal conductance was 320 mmol H2O m-2 s-1, and the range was between 173 and 477 mmol H2O m-2 s-1. A significant positive association between photosynthetic rate and yield was found for the hop cultivars.
Kenny, S.T. (2005). PHOTOSYNTHETIC MEASUREMENTS IN HOP (HUMULUS). Acta Hortic. 668, 241-248
DOI: 10.17660/ActaHortic.2005.668.31
genetic variability, Humulus lupulus, photosynthesis, stomatal conductance

Acta Horticulturae