Genotypic and environmental effects on guayule (Parthenium argentatum) latex and growth

Guayule (Parthenium argentatum Gray) is the best potential source of hypoallergenic latex to replace latex products from the Hevea (Hevea brasiliensis) plant that cause Type I allergies. However, information is not available on environmental effects on latex content and growth of newly released germplasm lines. This knowledge is needed to enhance guayule breeding efforts. The objectives of this study were to evaluate the genotype, environment, and genotype × environment effects on latex content and plant growth of guayule. Four lines were planted in the field at Maricopa, Arizona, USA on 6 April 1995 and 6 March 1996 and at Marana, Arizona, USA on 11 April 1995 and 12 June 1996. Plant height and width measurements were made in the spring of 1997 and latex content and biomass determined in the spring of 1997 and 1998. The main factors that included location, line, and plant age were significant and the interactions not significant for all traits measured. Environment accounted for over 50% of the variability observed in all traits, followed by plant age (16%) and line (10%). These results point to the tremendous impact that environment has on guayule plant growth, biomass, and latex content. We could not determine from these tests whether temperature, soil type, moisture, fertility, or a combination of these or other environmental factors were responsible for this response. Some of the non-significant interactions may have been significant if a larger or wider germplasm base could have been evaluated. Additional studies are needed to determine the environmental factor(s) responsible for the large environmental response we observed.