Effects of maize chlorotic mottle virus and potyvirus resistance on maize lethal necrosis disease

Authors: GENTZEL, IRENE - The Ohio State University; PAUL, PIERCE - The Ohio State University; WANG, GUO-LIANG - The Ohio State University; Ohlson, Erik

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2023
Publication Date: 2/26/2024
Citation: Gentzel, I.N., Paul, P.A., Wang, G., Ohlson, E.W. 2024. Effects of maize chlorotic mottle virus and potyvirus resistance on maize lethal necrosis disease. Phytopathology. 114(2): 484-495. https://doi.org/10.1094/phyto-05-23-0171-r .
DOI: https://doi.org/10.1094/phyto-05-23-0171-r 

Interpretive Summary: Maize lethal necrosis (MLN) is a devastating virus disease of corn caused by co-infection by maize chlorotic mottle virus (MCMV) and a potyvirus such as sugarcane mosaic virus (SCMV). The disease was first discovered in the 1970s in the United States and has since been found in Asia, Africa, and South America where it has caused massive yield losses. The most effective management of this synergistic virus disease is achieved by growing virus resistant corn lines. Identifying the most effective virus resistance genes is critical for developing improved corn varieties. In this study, we examined how different virus resistance genes affect virus levels in several corn lines. SCMV levels were up to two-million-fold lower in the most resistant line compared to the most susceptible. The degree of SCMV resistance closely correlated with higher expression of the potyvirus resistance gene known as Scmv1. Reduced MCMV virus levels were present in MCMV resistant corn lines at early time points, but at later stages of infection similar levels of MCMV were found among resistant and susceptible corn lines despite few or no observable disease symptoms. High levels of SCMV resistance were particularly important for reducing MLN disease severity and sufficient to eliminate any detectable synergy between the two viruses. These results indicate combining potyvirus and MCMV resistance in new corn varieties is an effective MLN management strategy. Seed companies can use this information to define novel breeding strategies which will increase yields for growers and improve global food security.

Technical Abstract: Maize lethal necrosis (MLN) is a viral disease caused by host co-infection by maize chlorotic mottle virus (MCMV) and a potyvirus, such as sugarcane mosaic virus (SCMV). In this study, we explore the impact of host resistance to SCMV and/or MCMV infection on plant disease, virus titer, and synergism during co-infection. In addition to visual assessment of disease progress, we used qRT-PCR to quantify relative virus titer and expression of known potyvirus resistance genes TrxH and ABP1. Relative to virus susceptible control inbred line Oh28, potyvirus and MCMV resistant lines were significantly more resistant to MLN. The cornbelt breeding line, N211, was completely asymptomatic to MCMV under singular infection. Tropical breeding line, KS23-6, was found to have the highest level of MLN resistance, though disease levels were similar to those found in N211 and another tropical breeding line, CML333. Only the dent corn inbred, Pa405, sustained resistance to SCMV in both the SCMV and MLN treatments. At early time points, MCMV titers in the resistant N211 and KS23-6 were more than 100,000-fold less than those found in the susceptible controls. However, despite no visible disease symptoms, these titer differences were no longer present by 14 days post inoculation. Consistent with previous reports, TrxH expression was significantly lower in Oh28 compared to other genotypes. Contrastingly, ABP1 was not as highly induced by virus infection as found previously. Both MCMV and potyvirus resistance in all combinations delayed disease progression, but temporal breakdown of resistance occurred in most cases. Although causative genes for MCMV resistance remain unreported, pyramiding multiple virus resistance loci is an effective strategy to develop lines with improved and durable disease resistance.