Evaluation of the Inhibitory Effects of Aqueous Extracts of Rhynchospora nervosa (Vahl) Boeckeler on the Germination and Initial Development of Cowpea (Vigna unguiculata (L.) Walp.)

Rhynchospora nervosa is a weed associated with infestations in economically important agricultural crops in several regions of Brazil. In this context, the present study aimed to perform phytochemical screening and evaluate the allelopathic effects of aqueous extracts from the aerial (AEAP) and underground (AEUP) parts of R. nervosa on the germination and initial development of cowpea (cultivar IPA 206). The presence of phenols, flavonoids, terpenes, and saponins was observed in AEAP, while only phenols were identified in AEUP. Furthermore, fractionation of the crude extract suggested the possible presence of kaempferol, a flavonoid, detected in the ethyl acetate fraction of the aerial parts of R. nervosa. At the highest concentration (100%), AEAP and AEUP inhibited cowpea seed germination by only 11.67% and 6.67%, respectively, when compared to the control treatment (0% inhibition). Furthermore, no significant differences were observed in the fresh and dry masses of seedlings exposed to the different concentrations of the extracts. Hypocotyl length increased significantly (above 8.25 cm) at all concentrations tested compared to the control (6.40 cm). The rootlets also showed significant growth (above 6.60 cm) compared to the control (4.43 cm). Based on these results, further investigation into the potential application of aqueous extracts of R. nervosa as biostimulants for cowpea, under both greenhouse and field conditions, is warranted.