Great Basin Naturalist


Rubber rabbitbrush (Chrysothamnus nauseosus [Pallas] Britt. ssp. viridulus) may prove to be a source of high-quality cis-isoprene rubber, but its establishment is limited by a lack of information on seed germination. Consequently, seeds were germinated at alternating temperatures (5–15, 5–25, 15–25, and 20–30 C) in light and dark as well as constant temperatures (15–40 C with 5-C increments) to determine temperature response. Seeds were also germinated in solutions of polyethylene glycol 6000 (0 to –5 bar), salinity regimes (1, 17, 51, and 86 mM) at all the above-mentioned temperatures to determine salinity and temperature interaction. The hormones GA3 (0, 2.9, 29.0, and 58.0 um) and kinetin (0, 4.7, 23.5, and 47.0 um) were used to study their effect on overcoming salt- and temperature-induced germination inhibition. Seeds of C. nauseosus ssp. viridulus were very sensitive to low temperature. Best germination was achieved at 25 and 30 C, but these seeds also germinated at a higher temperature (35 C). The seeds of rabbitbrush germinated at both constant and alternating temperatures. Light appears to play little or no role in controlling germination of the seeds of rubber rabbitbrush. However, seeds of rabbitbrush were sensitive to salinity, and seed germination was progressively inhibited by increase in salt concentration, although a few seeds still germinated at the highest saline level. Progressively higher concentrations of polyethylene glycol also progressively inhibited germination. Suppression of seed germination induced by high salt concentrations and high temperatures can be partially alleviated by the application of either GA3 or kinetin.