Effects of temperature and salinity on germination of non-pelleted and pelleted guayule (Parthenium argentatum A. Gray) seeds

Authors: Sanchez, Paul; CHEN, MEI-KUANG - University Of Arizona; PESSARAKLI, MOHAMMAD - University Of Arizona; HILL, HANK - Seed Dynamics, Incorporated; GORE, MICHAEL - Cornell University; Jenks, Matthew

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2014
Publication Date: 3/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58566
Citation: Sanchez, P.L., Chen, M., Pessarakli, M., Hill, H., Gore, M.A., Jenks, M.A. 2014. Effects of temperature and salinity on germination of non-pelleted and pelleted guayule (Parthenium argentatum A. Gray) seeds. Industrial Crops and Products. 55:90-96.

Interpretive Summary: Guayule Parthenium argentatum A. Gray is an important domestic source of natural rubber. Commercial field plots are currently established using greenhouse grown seedlings hand sown as plugs. However, this practice is expensive and laborious. Direct sowing of guayule seed in the field would reduce time and cost significantly, and yet the effects of seed pelleting, temperature, salinity level, and their interactions on seed germination and germination after induced dormancy of P. argentatum are not well established. To test germination requirements, raw (non-pelleted) and pelleted seeds were exposed to solutions having electrical conductivity (EC) of 0, 2, 4, 6, 8, and 10 mS/cm at 10, 20, 30, and 40ºC for 7 days. After treatment, the ungerminated seeds were transferred to 20oC and germinated in distilled water. Seed pelleting, temperature, salinity, and their interactions significantly affected seed germination of P. argentatum. The conditions for seed germination of raw and pelleted seeds having highest germination rates occurred at 20ºC, while salinity above EC 0-2 mS/cm increasingly suppressed germination. In addition, the lowest and highest temperature treatments at 10ºC and 40ºC, respectively, induced seed dormancy. Pelleted seeds of P. argentatum performed better than raw seeds in all treatments. Results presented here provide important new insights that can guide optimum seasonal and soil conditions for field establishment using new direct seeding methods.

Technical Abstract: Guayule (Parthenium argentatum A. Gray) is an important domestic source of natural rubber. Commercial field plots are currently established using greenhouse grown seedlings that are hand sown as plugs. However, this practice is expensive and laborious. Direct sowing of guayule seed in the field would reduce time and cost significantly, and yet the effects of seed pelleting, temperature, salinity level, and their interactions on guayule seed germination are not well established. To test germination requirements, non-pelleted (control) and pelleted seeds were planted in solutions having electrical conductivity (EC) of 0, 2, 4, 6, 8, and 10 mS/cm at 10, 20, 30, and 40 ºC for 7 days. After 7 days, the non-germinated seeds were transferred to distilled water plates in a 20 ºC environment. Seed pelleting, temperature, salinity, and their interactions significantly affected guayule germination. The optimal conditions for seed germination (i.e., highest germination rates) was found to be 20 ºC and EC 0-2 mS/cm, regardless of pelleting. Both temperature and salinity delayed germination and decreased viability. Germination was inhibited at both 10 and 40 ºC. Salinity effects on seeds decreased as germination temperature became optimal. Lowest germination percentages were observed at 6-10 mS/cm and at 30 and 40 ºC. Germination percentages increased for treatments after seeds were transferred to optimal conditions. Importantly, pelleted guayule seeds had exhibited higher germination than non-pelleted seeds in all treatments. Our results presented here provide important new insights that can help guide the selection of optimal seasonal and soil conditions for field establishment with new direct seeding methods.