Guayule seed germination under different conditioning treatments

Guayule (Parthenium argentatum Gray), a latex producing shrub from northern Mexico and southwestern Texas, has been considered a viable alternative commercial crop for arid lands throughout the world. Stand establishment by direct seeding has been ineffectual because of problems with seed germination. Seed dormancy has been ascribed as one of the main reasons for low germination. Special seed treatments, such as physical and chemical conditioning, have been devised to overcome embryo and seed coat dormancy, thereby improving germination and emergence. However, the treatments described in the literature have not been as effective as expected, and many of them are costly and time consuming. The objective of this study was to determine the effects of nine preconditioning treatments on the percentage and rate of germination and emergence, and seedling fresh weight. Three-year-old seed of lines AZ-101, AZ-3, and N9-3 were analyzed with X-ray to determine the seed lot quality. The results showed differences in quality (defined as seeds containing embryos and endosperm) among the three lines; however, no differences were found for percentage and rate of germination and emergence, and seedling fresh weight among the nine treatments. These results suggest that in older seed lots seed quality is of greater importance in determining germination and emergence than conditioning treatments.