Dormancy breaking and germination techniques for Dichanthelium leibergii, a cool season prairie grass

AcknowledgmentsThanks to Stuart Wagenius for help with experimental design and data analysis; C. Thomas, B. Barak, D. Sollenberger, and D. Herendeen for knowledge and advice; Team Echinacea for help in the field. This project was supported by the National Science Foundation, Grants 0545072, 0544970, & 1052165.

Maria Wang, Northwestern University & Chicago Botanic Garden

IntroductionDichanthelium leibergii is a prairie grass that was once common across the Midwest, but populations are now rare and isolated. It flourishes in high quality prairie remnants but is sparse in degraded habitats. D. leibergii is infrequently used in restorations, perhaps partly because its basic biology is not well characterized. There is little specific information on germination of D. leibergii. Stratification (storage in cold, moist conditions)1,2 and scarification (removal of seed coat)1,3,4 are two dormancy-breaking treatments shown to improve germination rates in other Dichanthelium species. My project aims to identify the dormancy-breaking treatments and germination conditions that maximize germination of D. leibergii. 

ResultsOverall germination rate was 17.4%. Scarification and stratification both affect germination rates and their effects are antagonistic (GLM with quasibinomial response, n = 30 dishes, 886 seeds, p < 0.0001). Germination temperature did not have a significant effect on germination rates.

Figure 1. D. leibergii inflorescence with flowering spikelets.

Figure 2. Predicted germination rate was highest for seeds that were scarified but not stratified (0.35 +/- 0.05), and lowest for seeds that were both scarified and stratified (0.05 +/- 0.02). All values reported are best-fit means with 1 s.e. based on the best model chosen by backwards elimination.

Figure 3. Newly emerged seedling from unscarified seed (left) and scarified seed (right).

Discussion• Scarification and stratification increased germination rates 3-4 fold when employed separately, but lowered germination rates when combined.• These findings provide useful information for restorationists or propagators hoping to grow D. leibergii, as well contribute to the understanding of this species and its genus.

Future directions• I am currently monitoring the growth and survival of these seedlings. • I will use these protocols in a germination experiment to investigate maternal line fitness differences in seeds collected from 5 different prairie remnants.

Figure 5. D. leibergii seedlings growing in plugs.

References 1 Freckmann, R. W. (1967). Taxonomic studies in

Panicum subgenus Dichanthelium. Ames, IA, Iowa State University. Ph.D. 

2 Spellenberg, R. W. (1968). Biosystematic studies in Panicum, group Lanuginosa, from the Pacific Northwest. Seattle, WA, University of Washington. Ph.D.

3 Lelong, M. G. (1965). Studies of reproduction and variation in some Panicum subgenus Dichanthelium. Ames, IA, Iowa State University. Ph.D.

Methods• Bulk collection of seeds were made from several prairie remnants in Minnesota during summer 2011• Random assignment of seeds to: 1) scarification: yes / no; 2) stratification: yes / no• Seeds were scarified by rubbing seeds against a metal sieve to break open seed coats• Seeds were stratified on moistened filter paper at 5°C in the dark for 8 weeks. Some seeds became inviable due to heavy mold growth.• Seeds were germinated on 1.5% agar under alternating light/dark regime, at 1) 25/15°C for 8/16h or 2) 20/10°C for 8/16h• Seedling emergence was recorded for 3 weeks

Study species:Dichanthelium leibergii•Cool season perennial•2 distinct flowering phases•Primary panicles produced mid-May through July, secondary panicles produced late June to September•Secondary panicales partially cleistogamous (closed-pollinated)

Stratification on agarA second experiment was performed to determine if stratification on agar would help control mold growth. Seeds were stratified on 1.5% agar for a month and germinated under the same conditions. Results: Mold levels were visibly lower on agar. Overall germination rate was 16.3%, but there was no significant effect of scarification or temperature (GLM with binomial response, n = 11 dishes, 294 seeds, p = 0.09 (scarification) and p = 0.4 (temperature).

SCARIFIED NOT SCARIFIED

0.0

0.1

0.2

0.3

0.4

Scarification

Ge

rmin

atio

n

stratifiednot stratified