In this study, it was found that 15 differentially expressed genes were significantly enriched in the MAPK signal transduction pathway of alfalfa seedlings treated with CaCl2 under salt stress, in the pathogen infection pathway, two genes (novel.4381, MsG0280006915.01) encoding LRR receptor-like serine/threonine protein kinase At3g47570 (FLS2), one encoding MPK3/6 gene mitogen-activated protein kinase 3 (MsG0480020857.01), and one encoding possible WRKY transcription factor 29 gene (WRKY29,MsG0080048967.01) regulate early virus defense and regulate plant stomatal development. This evidence concerns the gene MAPK3 and infection.