Evaluation of seed treatments for improved germination of starry rosinweed (Silphium asteriscus)

Abstract

Starry rosinweed (Silphium asteriscus) is a native wildflower of Florida’s pine flatwoods. This herbaceous perennial reaches 3 to 5 ft and bears yellow ray florets from May through September. Starry rosinweed is gaining popularity as a landscape plant, but there is little information available that describes methods for propagating this species by either sexual or asexual means. The objective of this study was to determine the effect of pretreatments on germination of S. asteriscus seeds. Seeds were collected in Sept. and Oct. 2008 and stored in polyethylene bags or moist stratified in potting media for 30 days at 39 °F. Subsequently, seeds that were stored in polyethylene bags at 39 °F were either water-soaked for 24 hours before planting or left dry. Before sowing, half of the seeds from each of the three previously described treatment combinations were cleaned by removing the pericarp to produce a total of six different treatment combinations that could affect seed germination. A second set of seeds was collected that were described as the fresh (not stored) sample. These seeds were either water-soaked or left dry. At planting time, half the seeds from each of these two treatments were cleaned by removing the pericarp. This resulted in four additional treatment combinations using fresh seed. All 10 treatment combinations were sown under greenhouse conditions (average temperature 73 °F). Separate and combined effects of storage, cleaning, and soaking were examined in an analysis that excluded seeds that were stratified. A second analysis looked at the combined effects of stratification and cleaning and excluded fresh seeds. The treatment that had the largest effect on percent germination and time to germinate was stratification. Mean time to germinate was 4.3 days for seed that received the moist-stratification treatment and a germination percentage of 93% was observed at 2 weeks. The time for seed to germinate was substantially slower and germination percentages were lower for all other treatment combinations that did not include stratification. Soaking and cleaning had some effect on germination rate. Storage and soaking affected the time for seeds to germinate when effects of stratification were excluded.