Defense Mechanisms Induced by DYDS and Dufulin Against Alfalfa Mosaic Virus (AMV) Infection in Cowpea

Alfalfa mosaic virus (AMV) is a devastating plant pathogen with an extensive host range, yet effective control strategies remain limited. This study investigated the prophylactic efficacy and molecular mechanisms of two plant immune inducers, the Paecilomyces variotii extract DYDS and the antiviral agent Dufulin, against AMV infection in cowpea (Vigna unguiculata). Our results demonstrate that both agents possess potent antiviral activity, with inactivation, protective, and therapeutic efficacies all exceeding 21.00%. Notably, DYDS exhibited superior overall performance. RT-qPCR and immunofluorescence assays confirmed a significant downregulation of AMV coat protein (CP) expression in treated plants. Furthermore, exogenous application of these inducers mitigated chlorophyll loss and markedly augmented the activities of key defense enzymes’ activity, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and L-phenylalanine ammonia-lyase (PAL), peaking at 5 days post-inoculation. In silico molecular docking simulations further revealed that DYDS and Dufulin interact spontaneously with the AMV-CP, yielding binding free energies of −6.5 and −5.8 kcal/mol, respectively. Gene expression analysis indicated that these inducers trigger a robust immune response through the integrated activation of the salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) signaling pathways. Collectively, these findings suggest that DYDS and Dufulin provide a dual mode of action—direct viral inhibition and host immune priming—offering a promising and sustainable approach for the management of AMV in leguminous crops.