Antifungal Activities of Isoflavonoids from Uromyces striatus Infected Alfalfa

Fungal pathogens constitute a severe yield‐limiting factor for the pasture crop alfalfa ( Medicago sativa L.). Eleven phenolic compounds, including a new isoflavane, were isolated from the Uromyces striatus Schroet . infected alfalfa. The effect of infection with U. striatus Schroet . on the phytochemical profile of alfalfa was investigated using ultra‐performance liquid chromatography (UPLC), and the antifungal properties of isolated compounds against a range of pathogens were tested. It was found that the contents of most of the isolated compounds in U. striatus infected alfalfa were higher than those in healthy alfalfa. Compounds 1–5 exhibited a moderate inhibitory activity against Curvularia lunata with 40.14±1.63 %, 48.03±1.22 %, 57.54±1.18 %, 50.10±1.56 %, and 61.54±2.14 % inhibition ratio at the concentration of 50 μg/mL. Compounds 3 and 5 showed a weak inhibitory activity against Fusarium graminearum with the EC 50 values of 104.2±2.66 and 123.0±1.23 μg/mL, and a moderate inhibitory activity against Bipolaris sorokinianum with the EC 50 values of 39.1±2.05 and 95.0±1.01 μg/mL, respectively. In pot experiments with wheat, compounds 1–5 possessed desirable protective efficacy of over 80 % and curative effectiveness of over 50 % against Puccinia striiformis f. sp. tritici at a concentration of 0.5 mg/mL