273 Delivery of water from roots to leaves through the xylem is critically important for maintenance of high yield of agricultural plants. This long-distance water transport is significantly affected by anatomi- cal traits of xylem conduits. Dimensions, shape and arrangement of xylem conduits influence both transport efficiency (i.e., the ability to transport water with minimal resistance) and safety (i.e., the ability to prevent embolism), as previously found in many studies (Sperry et al. 2005, Wheeler et al. 2005, Hacke et al. 2006). Confident determination of structural properties of xylem conduits (e.g. length, diameter) can be useful for estimation of their hydraulic resistance to sap flow (Sperry et al. 2005, Christman and Sperry 2010) as well as vulnerability to dysfunction due to cavitation (Tyree and Sperry 1989, Hacke and Sperry 2001). Anatomical structure of xylem belongs to well genetically fixed traits and, thus, large differences exist among plant species (Wheeler et al. 2005, Choat et al. 2007). However, little is known about intraspecific variability of the xylem traits. Results of the comparative study with various peach root- stocks showed a positive correlation between mean diameter of xylem vessels in stems and vigour of the plant (Tombesi et al. 2011). Architecture of xylem may be also related to plant water use as found in two cultivars of grapevine. Cultivar Grenache with higher hydraulic conductivity of xylem showed lit- tle changes in leaf water potential during the day in contrast to cultivar Syrah with lower hydraulic conductivity (Schulz 2003). These few examples il- lustrate that structure of xylem plays an important role in plant water relations and can be potentially Inherent variability in structural and functional traits of xylem among three hop varieties R. Jupa 1 , M. Baláž 1 , P. Svoboda 2 , V. Gloser 1 1 Masaryk University, Faculty of Science, Department of Experimental Biology, Brno, Czech Republic 2 Hop Research Institute, Žatec, Czech Republic ABSTRACT Intervarietal diferences in xylem structure could signifcantly afect water transport as well as vulnerability to cavitations and thus crop yield. Evaluation of crop varieties with respect to the specifc traits can be thus helpful in breeding and agricultural practice. In the present study we compared basic anatomical traits (vessel length and diameter) as well as theoretical and measured hydraulic conductivities (K) of xylem in stems of three hop varie- ties (Agnus, Saaz hop – Osvald’s clone 31, Vital). Tere were no statistically signifcant intervarietal diferences in measured K (overall mean 1.68 × 10 –6 m 4 /MPa/s), the ratio between K and theoretical conductivity (mean = 0.194), as well as vessel diameter and vessel length distributions. Te only noticeable diference was in the distribution of vessels with the diameter ≥ 100 µm which difered in Vital compared to Agnus or Osvald’s clone 31 (Kruskal-Wallis test, P < 0.001). Our results thus indicate highly conservative nature of xylem basic functional and anatomical char- acteristics in hop varieties studied. Keywords: Humulus lupulus; hydraulic conductivity; vessel diameter; vessel length Supported by the Czech Science Foundation, Grant No. 206/09/1967. Plant Soil Environ. Vol. 59, 2013, No. 6: 273–279