Different phytotoxic effect of Lolium multiflorum Lam. leaves against Echinochloa oryzoides (Ard.) Fritsch and Oriza sativa L

Rice cultivation, particularly prone to weed issues, requires practices able to effectively control them, however reducing the use of herbicides, responsible for damage to human health and ecosystem sustainability. Alternative strategies for weed management can be based on plant-plant interaction phenomena. In this context, a group of organic farmers has developed a pragmatic approach for weed containment using Lolium multiflorum Lam. as a cover crop before rice. The present study aimed to confirm the farmer field observations reporting a preferential inhibitory effect of L. multiflorum on Echinochloa oryzoides (Ard.) Fritsch, one of the most yield-damaging rice weed, compared with Oryza sativa L. The study showed that L. multiflorum was able to significantly reduce the seed germination of E. oryzoides. It was found to be more susceptible than O. sativa both to the effect of the aqueous extract and powder of L. multiflorum leaves (23-79% vs. 3-57% and 26-100% vs. 23-31%, respectively). In addition, the leaf extract was able to affect E. oryzoides growth starting from 20% concentration both in relation to the root and shoot length while O. sativa exhibited differences compared with the control only under the influence of extract 50%. The L. multiflorum leaf characterization by NMR and UPLC-HR-MS analyses led to the identification of 35 compounds including several polyphenols, glycosyl flavonoids and glycosyl terpenoids, as well as different amino acids and organic acids. Some of them (e.g. protocatechuic and gallic acids) are already known as allelochemicals confirming that L. multiflorum is a source of plant growth inhibitors.

Keywords: Allelopathy; Cover crop; Early watergrass; Italian ryegrass; Organic rice; Weed biocontrol.