Guayule (Parthenium argentatum Gray) has been produced as an alternative natural rubber crop in the U.S. for over 100 years with varying success. Selecting and breeding for higher yielding rubber and latex has been a priority for establishing guayule as a feasible alternative rubber and latex source, but many environmental conditions affect yields. Previous research has shown regional variability which means regional evaluation of guayule should be conducted for optimal regional line selection. Readily available lines, AZ1 - AZ4, and 11591, among others, were evaluated in the Southern High Plains over 20 years ago. Since then, newer lines have been developed with higher latex yields and quality. Therefore, an experiment was designed to evaluate three of these lines (E002, E003, E004) in greenhouse conditions. Growth parameters, health ratings, canopy temperatures, and bark thickness were measured regularly. Lines E003 and E004 had significantly larger canopy circumferences and plant height than line E002, however, plant health rankings were higher in E003 followed by E002, then E004 lines. Trunk diameter was also greater in E003 and E004 lines, but bark width did not significantly vary among treatments. Bark parenchyma cells are the site of rubber particle production, and therefore as bark thickness increases, rubber may also increase. These results indicate that while the E003 and E004 lines are larger, the rubber production may be higher in E002 in comparison. Many other factors continue to be examined, but these preliminary results further illustrate that line selection is essential, and overall biomass may not be the best factor for selecting high yielding lines.
