2017 ASHS Annual Conference

Guayule (Parthenium argentatum) is a woody desert shrub grown in the Southwestern U.S. for natural rubber, and organic resins and biomass used for energy and biofuel production. Improvements in cultural practices and breeding are being made to optimize yields in new cultivation areas, leading to more efficient processing. Flowers (peduncles and inflorescences) can account for up to 9% of the total biomass, thus by reducing or eliminating flower production, we hypothesized that photosynthates would be allocated to secondary compounds and/or biomass. In order to investigate the relationship between flowering and resource allocation, a field trial was carried out for three years with six guayule varieties and four replications. Treatments were cut (flowers removed by hand once per week) and uncut (allowed to flower without interference). The first harvest was at 14 months of age in the spring, and the next two harvests were each one year apart. Measurements taken were height, width, and fresh weight at harvest. Samples were analyzed for rubber, resin, and latex. Yields were calculated on a dry weight basis.

Although there were differences between varieties, there were no significant interactions between treatment and variety for any variable. At year one, rubber yield was significantly greater in the cut treatment, even though percent rubber and biomass yield were not. Percent resin, but not yield, was higher in year two in the cut plants. By year three, all variables except biomass and resin yield were higher when flowers were removed. Combined data from all three years showed the same trends. There were differences between treatments for some measured characteristics, but the differences were not great enough to warrant mechanical cutting of flowers on a field scale. However, genetic modification might be applied, for instance up-regulating a gene such as miR156, which has increased biomass significantly and created non-flowering switchgrass.