The resistance of alfalfa to downy mildew induced by oxalic acid

In order to determine if exogenous oxalic acid (OA) can induce alfalfa resistance to downy mildew, different OA concentrations including 10, 20, 30, 40 mmol·L-1 were sprayed on alfalfa seeding at 10-leaf stage. Disease index of alfalfa downy mildew was surveyed after treatment 7 days, activities of peroxidase (POD), phenylalanine ammonialyase (PAL) and superoxide dismutase (SOD) were analyzed after treatment 1 days, 3 days, 5 days, 7 days and 9 days. The results indicated that the 10~40 mmol·L-1 OA solution can reduce alfalfa downy mildew disease index and the disease index decreased with the OA concentration increased. The relative induced resistance increased with the maximum value of 50.8%. The POD, PAL and SOD activities in alfalfa leaf increased.