Seed age changes the germination response of weed species to cereal rye allelopathy

Authors: JACKSON, ALIYAH - North Carolina State University; MOORE, VIRGINIA - Cornell University; REBERG-HORTON, S. CHRIS - North Carolina State University; Mirsky, Steven; LEON, RAMON - North Carolina State University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2025
Publication Date: 10/6/2025
Citation: Jackson, A.W., Moore, V.M., Reberg-Horton, S., Mirsky, S.B., Leon, R.G. 2025. Seed age changes the germination response of weed species to cereal rye allelopathy. Weed Science. 73(1). Article e96. https://doi.org/10.1017/wsc.2025.10062.
DOI: https://doi.org/10.1017/wsc.2025.10062

Interpretive Summary: Cover crops, which are plant species grown when cash crops are not present (e.g., over winter), can provide cropping system benefits including weed suppression. Cereal rye is the most commonly planted cover crop; it can affect weeds through chemicals it produces ("allelopathy"). Weed seeds are potentially particularly vulnerable to allelochemicals produced by rye. This study investigated the allelopathic effects of rye roots on germination in the lab of Palmer amaranth, hairy crabgrass, giant foxtail, and lettuce seeds of varying levels of vigor. "Aged" (less vigorous) seeds exhibited 31% lower total germination than non-aged seeds. The extent of the response was species dependent. Giant foxtail actually had increased germination in the low allelopathy treatment compared to the control. The high allelopathy treatment reduced total germination of hairy crabgrass by less than 10%. Palmer amaranth was the least susceptible of the species to allelopathic compounds, regardless of level of seed vigor. Germination rate was reduced by seed aging and to a lesser extent by allelochemicals. This work provides guidance to farmers as to the likelihood of rye helping with weed suppression through allelopathy; it suggests that incorporating allelopathic rye varieties into cover crop rotations can reduce weed populations, but the age structure of the seed bank may determine the importance of allelochemicals for weed emergence.

Technical Abstract: Cereal rye (Secale cereale L.) is grown as a cover crop due to its ability to enhance soil health and suppress weeds through allelopathy, but germination responses of different weed species to allelochemicals have not been studied for seeds varying in age and consequently vigor. This study investigated the allelopathic effects of cereal rye on the germination of Palmer amaranth (Amaranthus palmeri S. Watson), large crabgrass [Digitaria sanguinalis (L.) Scop.], giant foxtail (Setaria faberi Herrm.), and lettuce (Lactuca sativa L.). Seeds were germinated in vitro in media with allelochemicals secreted by roots of cereal rye lines varying in allelopathic activity. Seeds were subjected to an accelerated aging treatment to modify their vigor. Results showed that aged seeds exhibited 31% lower germination than non-aged seeds. The magnitude of the germination reduction due to the presence of allelochemicals was species dependent. In the absence of allelochemicals, L. sativa exhibited a 20% reduction in germination due to aging, while the reduction was greater than 60% when allelopathy and aging were combined. Non-aged S. faberi seeds increased germination under low allelopathy conditions, with 20% greater germination compared with the non-treated control. Digitaria sanguinalis did not respond to seed aging, and the high allelopathy treatment reduced germination less than 10%. Amaranthus palmeri exhibited the highest germination and was the only species that was not affected by the seed aging and allelopathy treatments. Germination rate was reduced by seed aging and to a lesser extent by allelochemicals. Results suggest that incorporating allelopathic S. cereale varieties in cover crop rotations can reduce weed populations. However, the age structure of the seedbank might determine the importance of allelochemicals for emergence at the species level, likely causing weed community shifts.