Influence of harvest timing and storage interval on rabbitbrush seed germination, emergence, and viability

Rubber rabbitbrush (Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & Baird [Asteraceae]) has potential for use in water-conserving landscapes, but poor seedling emergence can be a problem for nursery production. We evaluated the effects of 1) harvest timing (stage of inflorescence maturity); and 2) duration of storage interval on seed viability, emergence, and germination for 6 geographically diverse populations. Stage of inflorescence maturity (harvest timing) had a statistically significant (P < 0.001) effect on seed germination and emergence, but across the harvest dates the trend was erratic and lacked identifiable biological meaning. Once the first seeds were ripe, germination and seedling emergence remained relatively constant throughout the harvest season. A 14-mo storage interval produced consistent and statistically significant (P < 0.001) effects on viability, germination, and emergence of seeds from all 6 populations. Seeds of all populations initially exhibited relatively low germination and emergence percentages, which increased to a maximum within 2 to 5 mo, and then slowly declined during the remainder of the 14-mo storage interval. Decline in germination percentage differed by population and ranged from 4 to 65%. In both experiments, seeds from populations of rubber rabbitbrush displayed very different seed germination and emergence percentages, with average germination under the various treatments ranging from 1.2 to more than 37.3%. When comparing testing methods, tetrazolium viability tests tended to overestimate seed germination, whereas seed germination was higher than seedling emergence. Viable seeds can be obtained from collections made during an extended harvest interval. Also, seeds can be stored at room temperature under ambient conditions with expectations of only minor losses of viability through 14 mo of storage, which should make possible 2 annual production cycles.