Guayule, Parthenium argentatum Gray, is a perennial shrub native to the Chihuahuan desert of Mexico and Texas. It is known for its latex and rubber production, which are viable alternatives to Hevea rubber. However, guayule seeds have low germination rate, which doesn’t meet commercial requirements. Guayule seeds have a germination rate between 55% and 87%, but this is highly dependent upon priming and soil temperature. Newer guayule lines have been developed, but the germination rate still varies. There is very little literature on successful priming methods in guayule seeds, most of which have been performed on historic lines in the 1980’s and 1990’s. To determine how newer lines are affected by different priming methods, we treated seeds with seven priming treatments and a control, then studied germination rates over 14 days. The treatments included: treatment 1 – control; Treatment 2 – Presoaking in 25% PEG, 10-4 M gibberellic acid, 0.05% KNO3, and 0.1% thiram fungicide adjusted to a pH of 8 with Ca(OH)2 and soaked for 4 days; Treatment 3 – Mildly scarified with fine sandpaper; Treatment 4 – Treatment 2 scarification; Treatment 5 –DI water soaking for 6 hours; Treatment 6 – Soaking with 75 ppm NAA and IAA, 1M KH2PO4 for 24 hours; Treatment 7 – Soaking in a DI water/ 0.1 M KNO3 solution for 12 hours; and lastly treatment 8 – Soaking in DI water for 8 hours, followed by soaking them for 2 hours in a solution of equal parts gibberellic acid (200 ppm) and 0.25% NaOCl. There were significant effects of treatment, line, and interactions of line and treatment on seed germination. Scarification had the overall highest germination percentage, followed by soaking in DI water for 6 hours and the control. The lowest germination was seen in lines soaked in DI water, followed by a bleach and gibberellic acid solution. Line E008 showed the highest germination rate, followed by E001, E009, E002, and E010. The interaction effects were highly variable, but indicated that each line was affected differently by the seed treatments. These results show that treatments to improve germination may need to be tailored to specific lines to optimize germination in guayule.
