Benzoxazinoids in roots and shoots of cereal rye (Secale cereale) and their fates in soil after cover crop termination

Authors: Rice, Clifford; OTTE, BRIANA - University Of Maryland; Kramer, Matthew; Schomberg, Harry; Mirsky, Steven; TULLY, KATHERINE - University Of Maryland

Submitted to: Chemoecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2022
Publication Date: 4/24/2022
Citation: Rice, C., Otte, B.A., Kramer, M.H., Schomberg, H.H., Mirsky, S.B., Tully, K.L. 2022. Benzoxazinoids in roots and shoots of cereal rye (Secale cereale) and their fates in soil after cover crop termination. Chemoecology. https://doi.org/10.1007/s00049-022-00371-x.
DOI: https://doi.org/10.1007/s00049-022-00371-x

Interpretive Summary: Cereal rye is a cover crop that has been shown to suppress weeds by producing compounds that inhibit germination and growth of several weeds. The weed suppressive compounds are produced in both roots and shoots and are released into the soil when rye cover crops are killed. Knowing the amounts and types of these compounds in rye tissues and how long they remain in the soil is important for devising weed control strategies. We determined the amounts of several weed suppressive compounds in rye at three times during the growing season and their longevity in soil after rye termination. In shoots, concentrations of the two most dominant compounds declined as rye matured, while in roots concentration of the most dominant compound was greatest at tillering. Concentrations of the compounds were much smaller in soil compared to shoots or roots. Once the rye was killed, the concentrations of all compounds increased in the soil where rye had been grown. Concentrations of most compounds decreased by half after four days. Most compounds were not detectable in the soil after 20 days. Information on the types and amounts of these compounds in shoots roots and their longevity in soil will be useful for breeders working to select new varieties of rye for weed suppression.

Technical Abstract: Cover crops provide agroecosystem services, such as weed suppression which can be exerted through release of allelopathic benzoxazinoid (BX) compounds. This research (1) characterizes changes in concentrations of BX compounds in shoots, roots, and soil at three growth stages (GS) of cereal rye (Secale cereale), and (2) their degradation following termination. Shoot dominant BX compounds, DIBOA-glc and DIBOA, concentrations were smallest at GS 83 (boot). Root dominant BX compound, HMBOA-glc, concentration was smallest at GS 54. Rhizosphere soil BX concentrations were 1000 times smaller than in root tissues. Dominant compounds in soil were HMBOA-glc and HMBOA. Concentrations of BX compounds were similar for soil near root crowns and between rows. Soil BX concentrations following rye termination declined exponentially in three treatments: incorporated shoots (S) and roots (R), no-till S+R (rye rolled flat), no-till R (shoots removed). On the day following rye termination, soil concentrations of HMBOA-glc and HMBOA in these three treatments increased above initial concentrations and were significantly greater than other BXs. Concentrations of these two compounds decreased the fastest while DIBOA-glc declined the slowest (half-life of 4 d) in no-till S+R soil. Concentrations of BX compounds were consistently small where shoots were placed on the surface of soil where rye had not grown. The short duration and complex dynamics of BX compounds in soil prior to and following termination illustrate the difficulty in enhancing weed suppression via targeted breeding for allelochemicals; valuable information for programs breeding for enhanced weed suppression by cereal rye.