Allelopathic effect of bergamot and pomegranate powders on the germination and seedling growth of two weeds associated with wheat

Weeds are one of the major biotic stresses for cultivated plants and constitute a challenge in crop management worldwide. Their infestation often undermines crop productivity through competition for primary resources, such as photosynthetically active radiation, water, nutrients, and space, ultimately causing loss to quantity and quality of the yield. The recent agricultural approaches aim to achieve safe management strategies in controlling weeds to decrease the harmful side effects of chemical herbicides. Allelopathy represents an alternative and environmentally friendly technique for the sustainable management of weeds, and its importance in agriculture is increasingly recognized. Allelopathy is the inhibitory/stimulatory effect of a donor plant on a receptor plant through the release of allelochemicals, produced by any part of plants through secondary metabolism pathways. These compounds belong to the classes of phenolics, terpenoids, and alkaloids and have been proved to interfere with germination and growth of weeds, acting as potential bioherbicides. A pot experiment was carried out under the greenhouse of the University of Foggia to investigate the possibility to control the germination and seedling growth of two wheat (Triticum durum Desf.) associated weeds, i.e., slender meadow foxtail or black grass (Alopecurus myosuroides Huds.) and annual rye-grass or italian rye-grass (Lolium multiflorum Lam.), using dried powders from epicarps of bergamot (Citrus bergamia Risso et Poit.) and pomegranate (Punica granatum L.). Cylindrical pots (20 cm height and 20 cm diameter) were filled with an equal amount of potting substrate and, except for the unweeded treatment (P0), powder from dried epicarps of bergamot (PBER) or pomegranate (PPOM) was applied at a rate of 10 g pot-1 as mulch in pre-emergence treatment. Then, 10 seeds of T. durum were sown 2 cm deep in each pot and, except for the weed-free treatment (W0), pots were infested with 30 seeds of A. myosuroides (WALO) or 30 seeds of L. multiflorum (WLOL) that were mixed thoroughly at 2 cm depth in the substrate. Moisture content in each treatment pot was kept constant at the water holding capacity, by restoring 100% of evapotranspiration losses measured on a daily basis by weighing the pots. The experiment was setup according to a factorial randomized block design with eight replications for each treatment and was terminated 52 days after sowing. The powders from bergamot and pomegranate epicarps significantly reduced the final germination percentage (FGP, %) of both A. myosuroides and L. multiflorum seeds, which also showed a significant increase of the mean germination time (MGT, days), along with a significant reduction of both germination index (GI, number of emerged seedlings/day) and seedling vigor index (VI). Both bergamot and pomegranate powder also had a reducing effect on the growth parameters of weeds, by significantly inhibiting root and shoot length. On the contrary, neither seed germination nor seedling growth of wheat were affected by powder addition to growth substrate. The obtained results indicate the allelopathic potential of powders from epicarps of bergamot and pomegranate in inhibiting the sprouting and seedling growing of A. myosuroides and L. multiflorum, while not causing damage to wheat plants.