Quantitative and Qualitative Variations in Resin Content and Guayulins (A and B) among Different Guayule Cultivars

Abstract

Guayule has substantial quantities of resin which is often discarded after rubber extraction. Resin from 13 cultivars of guayule from India was analyzed for its qualitative and quantitative variations. Stem had 6.15% resin followed by roots (5.91%), branches (5%), leaves (3%), and flowers (3.06%). Resin percent varied significantly among the cultivars. It varied from 10.7% in USDA-10 to 5.5% in UCR-1 ; however, resin synthesis and biomass of the shrub had poor correlation. Guayulins (sesquiterpene cinnamic acid esters) were analyzed by HPLC. Composition of guayulins varied among cultivars. Guayulin A was in the range 0.27-3.7 g/plant, the lowest being in USS2X and the highest in USDA-17. Regression analysis between resin yield and guayulin A as well as guayulin B per plant showed poor correlation. Guayulin A dominated over guayulin B in all plant parts analyzed. Variation in resin percentage and guayulin composition in different cultivars may be due to differences in the origin of the cultivars and not necessarily due to temperature or other environmental factors. Resin synthesis appears to be independent from rubber synthesis and is not influenced by temperature minima, which is obligatory for cis-polyisoprene biosynthesis.