Latent infection is the state in which a host is infected with a pathogen but does not show symptoms and persists until signs or symptoms are prompted to appear by environmental or nutritional conditions. Bioassay and histological method as well as serological techniques can be used to detect latent infection. Latent infection is common by diverse species of pathogens. Colletotrichum gloeosporioides, Alternaria alternata, Phomopsis leptostromiformis, Leptosphaeria maculans, Dothiorella gregaria, Glomerella cingulata and Lophodermium spp. etc. can persist on various hosts such as fruit trees, crops or trees. Research about latent infection is important in control of plant disease and in the breeding for resistance to a pathogen.