Differential influence of shoot extracts of winter cover crops on seed germination of corn, soybean and indicator plants

Abstract

The objective was to test the response of summer crops (Zea mays and Glycine max) and indicator plants to exposure to extracts of winter cover crops (Avena sativa, Lolium multiflorum and Triticum aestivum) regarding on seed germination. Bioassays were carried out to test six shoot extract concentrations, by using germitest paper maintained in controlled conditions. Zea mays, Glycine max, Lactuca sativa and Phalaris canariensis showed differential response to exposure to shoot extracts of Avena sativa, Lolium multiflorum and Triticum aestivum regarding on seed germination. Shoot extracts of Avena sativa and Lolium multiflorum increased seed germination while shoot extract of Triticum aestivum reduced seed germination of Zea mays. Shoot extracts of Avena sativa, Lolium multiflorum and Triticum aestivum reduced seed germination of Glycine max, Lactuca sativa and Phalaris canariensis. Highlighted ConclusionWinter cover crops can show different allelopathic potential on summer crops.Cover crops (e.g. winter crops) have several beneficial effects on agricultural fields (Kunz et al. 2016), including the weed suppression (Brust et al. 2014, Jabran et al. 2015 provided, among other reasons, by the release of allelopathic substances from cover crops and/or crop residues (Farooq et al. 2011) into the soil via leachates or root exudates, or by decomposition of plant biomass (Bonanomi et al. 2006). The allelopathic substances (e.g. phenolics, flavonoids or terpenoids - Macías et al. 2007), that can be synthesized in leaves, fruits, roots or seeds (Radosevich et al. 2007), may influence weed seed germination (Kunz et al. 2016) and/or inhibit weed plant growth (Farooq et al. 2011). However, the inhibitory effects may also influence, in different ways and intensities, on the subsequent summer crop (as reviewed by Shah et al. 2016).In the Southwest of Brazil, oat (Avena sativa) and wheat (Triticum aestivum) are commonly cropped as winter crops, and ryegrass (Lolium multiflorum) is normally used as a winter pasture. So, these species can be considered as winter cover crops preceding summer crop seeding. Summer crops, such as corn (Zea mays) and soybean (Glycine max), are commonly seeded into straw residues of winter cover crops. Thus, we hypothesized that winter cover crops can show differential allelopathic potential on subsequent summer crops (in a crop rotation system). The objective was to test the response of summer crops to exposure to extracts of winter cover crops regarding on seed germination. MATERIAL AND METHODSAn experiment was carried out to test the allelopathic potential of shoot extracts of oat, ryegrass and wheat, winter cover crops, on seed germination of corn, soybean -summer crops -lettuce (Lactuca sativa) and birdseed (Phalaris canariensis) -indicator crops. Bioassays were conducted using germitest papers soaked with distilled water and five concentrations of shoot extracts of each winter cover crop [2.5 times in relation to paper mass, according to Brasil (2009)]. Fifty seeds (replicated four times) of summe...