Flavonoid profiling and nodulation of some legumes in response to the allelopathic stress of Sonchus oleraceus L

Annual sowthistle (Sonchus oleraceus) has been reported to produce allelopathic effects. Two greenhouse experiments were conducted to estimate the allelopathic potential of both plant residue and root exudates of S. oleraceus on flavonoid composition and nodulation in a leguminous crop, Trifolium alexandrinum, and in two leguminous weeds, Melilotus indicus and T. resupinatum. The results of high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) showed that all three legumes contained six flavonoid aglycones: apigenin, daidzein, kaempferol, luteolin, myricetin and quercetin; and seven flavonoid glycosides: daidzin, genistin, hesperidin, hyperoside, kaempferol-7-O-glucoside, naringin and rutin. In general, both plant residue and root exudates had inhibitory effects on the flavonoid composition and nodulation of the target species. However, residue of S. oleraceus caused a significant increase in both individual and total detected flavonoids in T. alexandrinum. The results suggest that the phytotoxins released from S. oleraceus may restrain the biosynthesis of flavonoids in the target species, whereas the accumulated flavonoids in T. alexandrinum are allelopathic-induced metabolites and suggest a resistance mode in this crop. Ke ywords: allelopathy, flavonoids, legumes, nodulation, Sonchus oleraceus Acta Botanica Brasilica 29(4): 553-560. 2015. doi: 10.1590/0102-33062015abb0153 Flavonoid profiling and nodulation of some legumes in response to the allelopathic stress of Sonchus oleraceus L. Nasr Hassan Gomaa1*, Mahmoud Omar Hassan1, Gamal Mohammad Fahmy2, Luís González3, Ola Hammouda1 and Atteya Mostafa Atteya1 1 Department of Botany and Microbiology, Faculty of Science, Beni-Suef University, Beni-Suef, 62511, Egypt 2 Department of Botany, Faculty of Science, Cairo University, Giza, 12613, Egypt 3 Universidada de Vigo, Edificio de Ciencias, As Lagoas-Marcosende, Vigo, E36310, Spain. * Corresponding author: [email protected] Introduction Fabaceae is one of the widespread plant families with approximately 19,325 species in 727 genera. (Lewis et al. 2005). Legumes receive considerable attention due to their potential as food, forage, fibers, agricultural fuel and fertilizer. In the Mediterranean croplands, leguminous crops are cultivated extensively for local consumption and export. They are also widely used as forage, e.g., Egyptian clover (Trifolium alexandrinum) which represents nearly a quarter of all Egyptian crops (Nassib et al. 1990). The family includes many excellent sources of bioactive compounds which are used in folk medicine and nutraceutical approaches (Lin & Lai 2006). The phytochemistry of the Fabaceae has been well explored, and many secondary metabolites –including flavonoids, alkaloids, phenylpropanoids, terpenes, amino acids, anthraquinones and others – have been reported (Wink 1988; 2003). Flavonoids represent one of the most ubiquitous groups of secondary metabolites in the plant kingdom (Aoki et al. 2000), and includes some 6000 chemical structures (Hichri et al. 2011). The structural diversity of these compounds contributes to their many physiological activities. For example, flavonoids play a key role in the establishment of the root nodules produced in these nitrogen-fixing plants (Stafford 1997), and in inducing the germination of pollen grains (Taylor & Jorgensen 1992; Napoli et al. 1999). They are also advantageous to human health, due to their antioxidant properties, in addition to their possible role in preventing certain intractable diseases (Tapas et al. 2008; Georgiev et al. 2014). In agricultural ecosystems allelopathic effects occur in the form of phytotoxic compounds either exuded from plants through their root and/or from their decaying residues in soil; these compounds have been found to disrupt seed germination and establishment in various target plants (Gawronska & Golisz 2006). Flavonoid biosynthesis is typically induced in response to both biotic and abiotic stressors (Abdel-Farid et al. 2009; Olsen et al. 2009), and while much is known, the profiling of flavonoids in response to allelopathy is still largely lacking. Knowledge of allelopathy as a biotic stress influencing flavonoid biosynthesis in legumes remains preliminary. Flavonoid production has been studied in many legumes (e.g., Shimada et al. 2000; Winkel-Shirley 2001; Kim et al. 2003; Sreevidya et al. 2006; Veitch 2007). However several species,