Seed germination ecology of meadow knapweed (Centaurea x moncktonii) populations in New York State, USA

Authors: DITOMMASO, ANTONIO - Cornell University; Milbrath, Lindsey; MARSCHNER, CAROLINE - Cornell University; MORRIS, SCOTT - Cornell University; WESTBROOK, ANNA - Cornell University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2020
Publication Date: 12/3/2020
Citation: Ditommaso, A., Milbrath, L.R., Marschner, C.A., Morris, S.H., Westbrook, A.S. 2020. Seed germination ecology of meadow knapweed (Centaurea x moncktonii) populations in New York State, USA. Weed Science. 69(1):111-118. https://doi.org/10.1017/wsc.2020.86.
DOI: https://doi.org/10.1017/wsc.2020.86

Interpretive Summary: Meadow knapweed is an emerging invasive weed of moist pastures and grasslands in northeastern North America. Seed dormancy and germination requirements greatly influence when and where seedlings can establish but are unknown for meadow knapweed. We studied the effects of temperature, light, cold and wet seed treatment, scratching of the seed coat, and meadow knapweed population on percentage germination. Higher temperatures, exposure of seeds to light, and pre-treating seeds to cold and wet conditions all increased germination rates. Scratching the seed coat did not increase germination, and population differences were minor. Some seeds germinated even at the coldest temperature in the dark. Meadow knapweed is capable of germinating under a broad range of environments, which may have facilitated its increase in recent decades.

Technical Abstract: The introduced meadow knapweed (Centaurea × moncktonii), a hybrid of black (C. nigra) and brown (C. jacea) knapweeds, is increasingly common in pastures, meadows, and waste areas across many states in the USA, including New York. We evaluated the effects of temperature, light, seed stratification, scarification, and population on percentage germination in four experiments over two years. Percentage germination ranged from 3–100% across treatment combinations. Higher temperatures (30:20ºC, 25:15ºC and sometimes 20:10ºC day:night regimes compared with 15:5ºC) promoted germination, especially when combined with the stimulatory effect of light (14:10 hr L:D compared with continuous darkness). Under the three lowest temperature treatments, light increased percentage germination by 15–86%. Cold-wet seed stratification also increased germination rates, especially at lower germination temperatures, but was not a prerequisite for germination. Scarification did not increase percentage germination. Differences between C. × moncktonii populations were generally less significant than differences between temperature, light, and stratification treatments. Taken together, these results indicate that C. × moncktonii is capable of germinating under a broad range of environments, which may have facilitated this species’ range expansion in recent decades. However, C. × moncktonii also shows evidence of germination polymorphism: some seeds will germinate under suboptimal conditions while others may remain dormant until the abiotic environment improves. Subtle differences in dormancy mechanisms and their relative frequencies may affect phenological traits like the timing of seedling emergence and ultimately shape the sizes and ranges of C. × moncktonii populations.