Variable seed quality hampers the use of Themeda triandra (Poaceae) for seed production, agriculture, research and restoration: a review

Abstract

Themeda triandra (Forssk.) is a tussock grass of international importance for its keystone role in grassy ecosystems and, hence, is often a focus for seed production, research and ecological restoration. However, these applications can be challenged by its seed biology, including seed dormancy and the variability of seed traits among populations. The literature on these topics has not been well synthesised. To address this, we reviewed the relevant literature for Themeda triandra seed and found that seed quality is often poor but highly variable, and there are no current quality-assurance standards. Seed characteristics such as weight, awn length and desiccation tolerance can vary with seed ploidy (i.e. the number of chromosome sets). Germination rates of fresh Themeda triandra seed can be as low as 5%, which may be due to seed dormancy. Dormancy varies among populations and with seasonal conditions, and a period of dry storage at room temperature for 8–10 months may be needed before it will reach its full germination potential. No single treatment is effective in overcoming dormancy across all populations. The application of gibberellic acid can increase germination by ~30% in some populations. Although plant-derived smoke products can be effective, they also lack standardisation. Other treatments including the application of heat, or wet–dry cycling warrant further investigation. We recommend the standardisation of Themeda triandra seed testing and labelling, which would allow end users to assess value for money when purchasing seed commercially.