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Recent Advances in Guayule Seed Germination Procedures¹

Guayule (Parthenium argentatum Gray), a xerophytic shrub native to northeastern Mexico and southern Texas, is receiving renewed attention as a potential source of natural rubber in the semiarid regions of the world. A major problem in propagating guayule is seed dormancy. The objectives of this investigation were to evaluate and modify old seed treatment methods and to develop an improved standard procedure for quick and complete germination of guayule seeds to enhance breeding and improvement of the crop. The optimum concentration of sodium hypochlorite (NaOCl) needed for breaking seed dormancy was higher for younger than older seeds. Seeds should be washed and soaked in distilled water for 8 hours followed by a 2-hour treatment with a solution of equal parts of gibberellic acid (200 ppm) and NaOCl (1.0% for fresh seeds, and 0.25% for 1-year-old seeds). With this procedure freshly harvested seeds germinated 100% under light and over 70% in complete darkness. Emergence of seedlings from soil depended primarily upon seed size. Large guayule seeds emerged better at all depths to 18 mm after standard treatment than did medium or small seeds.

Key Words: Parthenium argentatum • Natural rubber • Semi-arid regions • Sodium hypochlorite • Gibberellic acid • Dormancy

² Research associate and senior biologist, respectively.

Received for publication December 4, 1979.