Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/18/2013
Publication Date: 2/9/2013
Publication URL: http://handle.nal.usda.gov/10113/57980
Citation: Gealy, D.R., Duke, S.E., Moldenhauer, K. 2013. Root distribution and potential interactions between allelopathic rice, sprangletop (Leptochloa spp.), and barnyardgrass (Echinochloa crus-galli) based on 13C isotope discrimination analysis. Journal of Chemical Ecology. 39:186-203. Interpretive Summary: Cultivars which carry traits that enable them to suppress weeds could improve the economical management and sustainability of rice production. Interactions between roots of rice and weeds are thought to be modulated by the weed-suppressive activity of some rice cultivars, but these phenomena are difficult to measure and not well understood. Above-ground crop-weed interactions and root distribution of PI 312777 and Taichung Native 1 (TN-1) (rice cultivars known to release weed-suppressive “allelochemicals” from roots), breeding selections, and non-suppressive commercial cultivars, and two weed species (sprangletop and barnyardgrass), were evaluated in field plots at Stuttgart, Arkansas. The allelopathic cultivars and other weed-suppressive cultivars produced more tillers and suppressed both weed species to a greater extent than other cultivars. Stable carbon isotope analysis of intermixed roots showed that the allelopathic cultivars produced more root weight near the soil surface compared to the non-suppressive cultivars, and barnyardgrass reduced rice yield and root mass more than did sprangletop. Our results demonstrated that roots of allelopathic cultivars such as PI 312777 and TN-1 grew more aggressively near the soil surface in the presence or absence of weeds as compared to non-suppressive cultivars. Rice plant types exhibiting similar root distribution and chemical exudation traits in combination with high tillering and yield might prove useful for improvement of natural weed suppression and management in organic rice or other reduced-input systems.
Technical Abstract: Weed-suppressive rice cultivars hold promise for improved and more economical weed management in rice. Interactions between roots of rice and weeds are thought to be modulated by the weed-suppressive activity of some rice cultivars, but these phenomena are difficult to measure and not well understood. Thus, above-ground productivity, weed suppression, and root distribution of 11 rice cultivars and two weed species were evaluated in a drill-seeded, flood-irrigated system at Stuttgart, Arkansas, USA in a two-year study. The allelopathic culitvars, PI 312777 and Taichung Native 1 (TN-1), three other weed-suppressive cultivars, three indica-derived breeding selections, and three non-suppressive commercial cultivars were evaluated in field plots infested with barnyardgrass (Echinochloa crus-galli (L.) Beauv.) or bearded sprangletop (sprangletop, Leptochloa fusca (L.) Kunth var. fascicularis (Lam.) N. Snow). The allelopathic cultivars produced more tillers and suppressed both weed species to a greater extent than did the breeding selections or the non-suppressive cultivars. 13C isotope discrimination analysis of mixed root samples to a depth of 15 cm revealed that the allelopathic cultivars typically produced a greater fraction of their total root mass in the surface 0-5 cm of soil depth compared to the breeding selections or the non-suppressive cultivars, which tended to distribute their roots more evenly throughout the soil profile. These trends in root mass distribution were apparent at both early (pre-flood) and late-season stages in weed-free and weed-infested plots. Cultivar productivity and root distribution generally responded similarly to competition with the two weed species, but barnyardgrass reduced rice yield and root mass more than did sprangletop. These findings have demonstrated for the first time that roots of the allelopathic cultivars PI 312777 and TN-1 explore the upper soil profile more thoroughly than do non-suppressive cultivars under weed-infested and weed-free conditions in flood-irrigated U.S. rice production systems. They raise the interesting prospect that root proliferation near the soil surface might enhance the weed-suppressive activity of allelochemical exudates released from roots. Plant architectural design for weed suppressive activity should take these traits into consideration along with other proven agronomic traits such as high tillering and yield.