Inter-population variation in seed longevity for two invasive weeds: Chrysanthemoides monilifera ssp. monilifera (boneseed) and ssp. rotundata (bitou bush)

Seed longevity has a major influence on the success of weed management and eradication programmes. A correlation between responses to a controlled aging test performed at 45°C, 60% relative humidity (RH) and seed persistence in the field has recently been suggested. Here we investigated whether collections of differing quality of two closely related invasive weeds, Chrysanthemoides monilifera ssp. monilifera and ssp. rotundata (boneseed and bitou bush, respectively), had different seed longevity using the controlled aging test. Chrysanthemoides monilifera ssp. monilifera fruits were collected from across five Australian states, and C. monilifera ssp. rotundata from one state, covering their invasive ranges. Seed quality was assessed visually and using tetrazolium staining, and a series of germination tests established appropriate germination conditions. The controlled aging test was run for a subset of collections. Chrysanthemoides monilifera ssp. rotundata seeds died more quickly (time to lose 50% viability, P₅₀ = 16 days) than the C. monilifera ssp. monilifera collections (P₅₀ = 47 days) when aged at 45°C and 60% RH. This difference was significant even considering the large differences in longevity between C. monilifera ssp. monilifera populations (P₅₀ = 35-61 days; probably due to differences in maturity at collection). Based on a published correlation, we predict that mature C. monilifera ssp. monilifera may have a long-lived (>3 years) seed bank and C. monilifera ssp. rotundata may have a transient (