Location: Corn, Soybean and Wheat Quality Research2022 Annual Report
Objective 1: Identify and characterize endemic and emergent viruses in corn and soybean, and develop sequence and detection resources. Sub-objective 1: Identify, diagnose, and characterize insect-transmitted pathogens of maize and soybean. Objective 2: Develop genetic markers and germplasm associated with corn virus resistance genes, and transfer information for practical management solutions. Sub-objective 2.A: Confirm the identity of HPWMoV resistance loci in maize and evaluate the effects of disease resistance on seed contamination and transmission. Sub-objective 2.B: Identify and characterize loci conferring tolerance/resistance to maize yellow mosaic virus. Sub-objective 2.C: Identify bean pod mottle virus resistant Glycine accessions and incorporate resistance into a cultivated soybean background. Objective 3: Fine map, clone, and characterize virus resistance genes, facilitating the investigation of host-pathogen interactions. Sub-objective 3.A: Fine map the WSMV resistance gene, wsm3, and examine pathogenesis of WSMV in resistant and susceptible maize. Sub-objective 3.B: Fine map MCMV resistance loci in maize inbred lines and develop near isogenic lines to study host-pathogen interactions.
Corn and soybean production in the United States is valued at more than $80 billion annually. Pathogens, including plant viruses, constitute a major component of crop loss, reducing U.S. corn and soybean yields by approximately 15%. Furthermore, pathogen contamination of grain poses major phytosanitary concerns for international trade. The spread of invasive pests and pathogens due to increased global trade and changing habitats, necessitates continued monitoring and identification of emerging viruses and their vectors to inform appropriate disease management strategies. The overarching goals of our research are to detect and characterize important viruses of corn and soybean, identify and develop virus resistant germplasm, map resistance loci, and elucidate mechanisms of host-vector-virus interactions. Using serological, molecular, and next generation sequencing techniques, we will identify key endemic and emerging maize and soybean viruses, evaluate virus population structures, and develop diagnostic assays. Host range and insect-vectors will be determined to reveal factors important for pathogenesis and transmission. We will identify resistant germplasm and develop molecular breeding tools to combat emerging maize viruses, such as high plains wheat mosaic virus (HPWMoV) and maize yellow mosaic virus (MaYMV). Secondary and tertiary soybean gene-pools will be evaluated to identify bean pod mottle virus (BPMV) resistant germplasm and resistance will be incorporated into cultivated soybean lines. Fine mapping and map-based cloning approaches will used to delineate the genomic loci associated with maize chlorotic mottle virus (MCMV) and potyvirus resistance genes, helping to determine mechanisms of host-resistance and to broaden our overall understanding of virus resistance in plants. Seed producers, breeders, researchers, and farmers will benefit from new disease diagnostic and molecular breeding tools, leading to improved corn and soybean yields.
This is the first report for this new project which began in March 2022 and continues research from the previous project, 5082-22000-001-00D, “Control of Virus Diseases in Corn and Soybean”. Please see the report for the previous project for additional information. The unit has made progress across all objectives during the first few months of the project and is on target to meet expected milestones. Objective 1, characterize endemic and emerging viruses in corn and soybean. Soybean seed exhibiting virus-like symptoms from a local elevator were tested for common soybean viruses using a variety of molecular and serological approaches. In collaboration with Ohio State University pathologists and entomologists, it was determined that the seeds were damaged by Cercospora, a fungal pathogen, as well as brown marmorated stink bug. The host range of maize yellow mosaic virus (MaYMV) was evaluated across related Poaceous crop and weed species and the virus infected several agronomically important hosts in addition to corn, wheat, and sugarcane, which have been reported on elsewhere. Additional MaYMV hosts include barley, millet, and oats as well as several grasses including ryegrass and switchgrass. Work is ongoing to identify additional insect vectors of this virus. The unit has developed and tested a purification protocol to isolate MaYMV virus particles. These purified virus particles will be used to generate antibodies and rapid serological diagnostic tests for the virus; the only currently available diagnostic tests are costly and laborious. Objective 2, develop genetic markers and virus resistant germplasm. A wheat curl mite colony was established and procedures for virus transmission by mites were developed and used to successfully transmit wheat streak mosaic virus (WSMV). The parents of the maize nested association mapping (NAM) panel and approximately 80 lines from the maize Goodman 282 association mapping panel were screened for resistance to MaYMV. Several asymptomatic lines were identified including at least one which had approximately 50-fold reduced virus titer when compared with susceptible controls. Previously reported bean pod mottle virus (BPMV) resistant, tolerant, and susceptible soybean and wild soybean species: G. soja, and G. tomentella, accessions were acquired from GRIN and seed was successfully multiplied for most accessions. Soybean susceptible controls were confirmed to be BPMV susceptible. Twenty-one G. soja lines were screened for BPMV and seven were found to display no visible symptoms. However, BPMV was detected among all lines by serological tests. Seven G. tomentella lines were screened for resistance to BPMV, among which six were found completely resistant by serological tests. Additional lines will be evaluated as seed becomes available. These lines have potential for use in developing soybean with improved BPMV resistance or tolerance. Objective 3, fine map, clone and characterize virus resistance genes. Fine mapping of the WSMV resistance gene is in progress. Approximately 100 families for which recombination occurred between the gene’s flanking markers were planted in the field and will be screened with WSMV. This experiment will further delineate the gene locus beyond the genomic interval we previously defined. A green fluorescent protein (GFP)-tagged WSMV construct that can be used to visualize virus localization using microscopy has been used to infect corn successfully and inoculum has been bulked up in preparation for experiments. Fine mapping of MCMV resistance loci is ongoing. Backcrossed B73 x CML333 plants were planted in the field to generate advanced backcrossed lines, mapping populations, and families to support efforts to fine map a chromosome 10 MCMV resistance gene. N211 x Oh28 backcrossed lines were also planted to generate mapping populations to fine map chromosome 3 and chromosome 5 MCMV resistance genes.