Plant-infecting viruses cause significant losses to agriculture, including to staple crops such as wheat, maize, and rice. Preventing and managing endemic and emerging plant diseases is an ongoing challenge. Maize lethal necrosis, or MLN, has emerged globally since 2010-2011 in East Africa, Asia, and South America. MLN is caused by synergistic co-infection of two viruses: maize chlorotic mottle virus (MCMV) and any of several maize-infecting potyviruses that are endemic worldwide--sugarcane mosaic virus (SCMV), maize dwarf mosaic virus (MDMV), Johnsongrass mosaic virus (JGMV), or wheat streak mosaic virus (WSMV). Although the route(s) of introduction and emergence of MLN are not fully elucidated, considerations for preventing plant pathogen introduction and managing disease once present, including diagnostics in global trade and genetic resistance in plants, will be discussed. In agricultural and uncultivated settings, mixed infections of viruses frequently occur with various possible outcomes. In the mixed infection of MCMV and a potyvirus, titer of MCMV increases and disease severity is strongly enhanced, with tissue and often plant death (lethal necrosis) that does not occur in single infections with either virus alone. Other viruses also coexist and frequently co-infect plants in field settings where MLN is emergent, including a recently discovered maize-infecting polerovirus, variously named maize yellow mosaic virus RMV2 (MYDV RMV2), maize yellow mosaic virus (MaYMV), and MYDV-like. Outcomes of mixed infections of MCMV, SCMV, and MaYMV show interactions of each virus but synergistic lethal necrosis only for the MCMV + SCMV combination.
1. Identify two or more ways in which plant viruses can be introduced to new locations.
2. Describe commonly-employed approaches to limit plant virus introduction and/or minimize losses caused by plant disease.
3. Describe two or more possible outcomes of virus mixed infections in plants.