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ARS Home » Southeast Area » Mississippi State, Mississippi » Crop Science Research Laboratory » Corn Host Plant Resistance Research » Research » Research Project #434375
Research Project: Enhanced Resistance of Maize to Aspergillus flavus Infection, Aflatoxin Accumulation, and Insect Damage

Location: Corn Host Plant Resistance Research

2019 Annual Report


Objectives
1. Identify new sources of maize germplasm with resistance to Aspergillus (A.) flavus infection and aflatoxin accumulation. We have developed and released maize germplasm lines with resistance to A. flavus infection and aflatoxin accumulation; however, germplasm with higher levels of resistance and different mechanisms of resistance are needed. We will evaluate germplasm obtained through the Germplasm Enhancement of Maize (GEM) project, the International Maize and Wheat Improvement Center (CIMMYT), and from other sources using methodologies developed in the research unit. Although we have developed effective procedures for inoculating plants with A. flavus and measuring aflatoxin, we will continue to evaluate other methods of quantifying resistance to increase efficiency and reduce costs. 2. Identify new sources of maize germplasm with resistance to fall armyworm, southwestern corn borer, and corn earworm. We have developed and released germplasm lines with excellent resistance to fall armyworm and southwestern corn borer leaf feeding damage using methodology for screening developed in the research unit. We will continue to screen germplasm from the GEM project, CIMMYT, and other sources to identify new sources of resistance to leaf feeding. We will also screen germplasm to identify sources of resistance to ear damage by fall armyworm, southwestern corn borer, and corn earworm. Because insect feeding provides a site for fungi to enter the developing ears of maize, resistance to ear-feeding insects should be reduced. 3. Develop and characterize genetic mapping populations, identify and elucidate functions of genes associated with resistance, and develop molecular markers for enhancing maize germplasm resistance to A. flavus/aflatoxin and insects. We have genotyped and phenotyped populations of F2:3 families to identify quantitative trait loci associated with resistance to aflatoxin accumulation and insect feeding, and additional populations are currently being developed. We have created near-isogenic lines (NILs) to validate the QTLs. We evaluated a 300-line association mapping panel for aflatoxin accumulation and ear damage by caused by insect feeding. From these studies we will identify and confirm additional QTL and candidate genes associated with resistance. We will investigate expression and function of these and other genes or groups of genes using a variety of techniques. 4. Develop and release maize germplasm with resistance to A. flavus infection, aflatoxin accumulation, and insect damage. Germplasm identified in Objectives 1 and 2 will be used in developing germplasm lines with resistance to aflatoxin accumulation and insect damage using conventional phenotypic selection. We will use information on molecular markers associated with resistance obtained from Objective 3 to enhance our efforts to produce better adapted lines with higher levels of pest resistance.


Approach
Objective 1: Identify new sources of maize germplasm with resistance to Aspergillus (A.) flavus infection and aflatoxin accumulation. Screen maize germplasm obtained from the Germplasm Enhancement of Maize project (GEM) project, International Center for Maize and Wheat Improvement (CIMMYT), and other sources for resistance to aflatoxin accumulation to identify new and potentially useful sources of resistance. Determine optimal combinations of A. flavus and A. parasiticus isolates for screening maize germplasm for resistance to aflatoxin accumulation under different environmental conditions. Objective 2: Identify new sources of maize germplasm with resistance to fall armyworm, southwestern corn borer, and corn earworm. Screen maize germplasm from CIMMYT, the GEM project, and other sources for resistance to leaf feeding by fall armyworm and southwestern corn borer. Screen maize germplasm for resistance to ear feeding by fall armyworm, southwestern corn borer, and corn earworm. Objective 3: Develop and characterize genetic mapping populations, identify and elucidate functions of genes associated with resistance, and develop molecular markers for enhancing maize germplasm with resistance to flavus/aflatoxin and insects. Identify genetic loci associated with resistance to A. flavus infection and aflatoxin accumulation via analysis of linkage and association mapping and sequencing data. Identify genetic loci associated with resistance to lepidopteran insect feeding via analysis of linkage and association mapping, pathway analysis, or sequencing data. Identify genes and elucidate functions of genes associated with resistance to A. flavus/aflatoxin and insects. Objective 4: Develop and release maize germplasm with resistance to A. flavus infection, aflatoxin accumulation, and insect damage. Develop and release maize germplasm lines with resistance to A. flavus infection and aflatoxin accumulation using conventional breeding methods, and develop and release lines with resistance to feeding by southwestern corn borer and fall armyworm using conventional breeding methods. Develop lines with resistance to A. flavus infection, aflatoxin accumulation, and insects using molecular markers and release together with marker information.


Progress Report
Seventy maize germplasm accessions obtained through the Germplasm Enhancement of Maize (GEM) project were evaluated for resistance to aflatoxin accumulation in field trials in 2018. Those that exhibited resistance to aflatoxin accumulation are being further evaluated in 2019. An additional 50 GEM accessions are being evaluated in 2019. Advanced generation maize breeding lines developed through multiple cycles of selection for resistance to aflatoxin accumulation were evaluated for aflatoxin accumulation in the 2018 field trials and are being evaluated again in 2019. Forty of the advanced breeding lines were evaluated as testcrosses for yield and other agronomic qualities in 2018, and some exhibited good combining ability for yield. A group of 45 maize hybrids developed by scientists in Texas, Georgia, and Mississippi were evaluated for resistance to aflatoxin accumulation at five locations in 2018. Those developed by ARS at Mississippi State, Mississippi, exhibited high levels of resistance. Phenotyping of four bi-parental populations (Mp715 × Va35, Mp717 × Va35, Mp717 × PHW79, and Mp705 × Mp719) for resistance to aflatoxin accumulation was completed in 2018. Quantitative trait loci (QTL) associated with resistance to aflatoxin accumulation were identified on Chromosomes 6 and 7 of Mp715 and Chromosomes 1 and 3 of Mp719. Analyses of the other populations to identify QTL associated with resistance are not complete. The results of a Genome Wide Association Study (GWAS) that was previously conducted to identify genes associated with resistance to aflatoxin accumulation were used to create a new analysis technique for identifying metabolic pathways associated with resistance. Near-isogenic lines (NILs) were created for 1-4 QTL associated with resistance and identified in the bi-parental population, Mp313E × Va35. A collaborator at Mississippi State University (6064-21000-015-05S) has completed whole genome sequencing of the parental lines, Mp313E and Va35, and is now sequencing the NILs to identify candidate genes associated with resistance and to generate molecular markers that can be used in developing hybrids with resistance to aflatoxin accumulation and other desirable agronomic qualities. In 2019, 300 maize germplasm lines were evaluated for resistance to fall armyworm leaf feeding damage. Leaf feeding damage was visually rated 14 days after infestation with 40 neonates per plant. Lines developed by ARS exhibited the highest levels of resistance to feeding, but other lines expressing high levels of resistance included CML333, CML139, CML67, CML122, CML484, CML332, and CML381. Results of this evaluation will be shared with cooperators at the International Maize and Wheat Improvement Center (CIMMYT) in Nairobi, Kenya (6064-21000-015-01R). Germplasm lines identified as most resistant will be used to produce resistant varieties and hybrids for African counties where fall armyworm is a devastating pest. Analysis of the bi-parental mapping population, Mp705 × Mp719, identified significant QTL for resistance to fall armyworm on Chromosomes 4 and 9 of Mp705 that together accounted for 35% of the phenotypic variance associated with damage.


Accomplishments
1. Metabolic pathway analysis technique developed for Genome Wide Association Studies (GWAS). Use of GWAS to identify genes affecting traits such as insect and disease resistance in corn or other crop plants is widespread, but results are frequently disappointing. Too many genes with small effects are usually identified, making it difficult for geneticists and plant breeders to choose plants with the best genes or combinations of genes for improving the trait of interest. ARS researchers at Mississippi State, Mississippi, created a technique for analyzing output from GWAS to identify metabolic pathways to which the genes belong. The analysis identifies a few important pathways that can be studied in depth to determine which genes are truly important in expression of the trait. By selecting specifically for the most important genes associated with the trait of interest, geneticists and plant breeders will be more effective in improving the trait. Use of this approach to plant breeding will enhance the efforts to make seed of corn hybrids with genetic resistance to insects and diseases commercially available to corn producers.

2. Quantitative trait loci (QTL) associated with resistance to fall armyworm damage identified. Fall armyworm is a major pest of corn in the southern United States. Its recent introduction into several countries in Africa and Asia has caused devastating losses in those countries. Fall armyworm larvae feed on all above-ground portions of the corn plant, causing losses in both yield and grain quality. ARS researchers at Mississippi State, Mississippi, have developed and released corn germplasm lines with resistance to fall armyworm damage. In a gene mapping study of a population of segregating families derived from the single cross, Mp705 × Mp719, they identified two QTL, regions of Chromosomes 4 and 9 of Mp705, that account for 35% of the phenotypic variance associated with fall armyworm leaf feeding damage. Using molecular markers, these QTL can be transferred into susceptible, but otherwise desirable and well-adapted lines, to enhance their resistance to fall armyworm damage. By using the lines with enhanced resistance as parents, hybrids with genetic resistance to fall armyworm damage can be produced and provided to farmers in not only the Unites States, but also countries in Africa and Asia where fall armyworm damage to corn has emerged as a serious problem.


Review Publications
Smith, J.S., Williams, W.P., Windham, G.L. 2019. Aflatoxin in maize: a review of the early literature from "moldy-corn toxicosis" to the genetics of aflatoxin accumulation resistance. Mycotoxin Research. 35:111-128. https://doi.org/10.1007/s12550-018-00340-w.
 Dhakal, R., Cgau, C., Karan, R., Windham, G.L., Williams, W.P., Subudhu, P. 2017. Expression profiling coupled with in-silico mapping identifes candidate genes for reducing aflatoxin accumulation in maize. Frontiers in Plant Science. 8:503. https://doi.org/10.3389/fpls.2017.00503.
 Womack, E.D., Warburton, M.L., Williams, W.P. 2018. Mapping of quantitative trait loci for resistance to fall armyworm and southwestern corn borer leaf-feeding damage in maize. Crop Science. 58(2):529-539. https://doi.org/10.2135/cropsci2017.03.0155.
 Meseka, S., Williams, W.P., Warburton, M.L., Brown, R.L., Ortega, A., Bandyopadhyay, R., Menkir, A. 2018. Heterotic affinity and combining ability of exotic maize inbred lines for resistance to aflatoxin accumulation. Euphytica. 214:184.
 Hawkins, L.K., Warburton, M.L., Tang, J., Tomashek, J., Alves, D., Ogunola, O.F., Smith, J.S., Williams, W.P. 2018. Survey of candidate genes for maize resistance to infection by Aspergillus flavus and/or aflatoxin contamination. Toxins. 10(2):61.
 Damianidis, D., Ortiz, B.V., Windham, G.L., Bowen, K.L., Hoogenboom, G., Scully, B.T., Hagan, A., Knappenberger, T., Woli, P., Williams, W.P. 2018. Evaluating a generic drought index as a predictive tool for aflatoxin contamination of corn: from plot to regional level. Crop Protection Journal. 113:64-74. https://doi.org/10.1016/j.cropro.2018.07.013.
 Christensen, S.A., Huffaker, A., Sims, J., Hunter Iii, C.T., Block, A.K., Vaughan, M.M., Willett, D.S., Mylroie, E., Williams, P.C., Schmelz, E.A. 2017. Fungal and herbivore elicitation of the novel maize sesquiterpenoid, zealexin A4, is attenuated by elevated CO2. Planta. 247(4):863-873. https://doi.org/10.1007/s00425-017-2830-5.
 Smith, J.S., Williams, W.P., Windham, G.L., Xu, W., Warburton, M.L., Bhattramakki, D. 2019. Identification of quantitative trait loci contributing resistance to aflatoxin accumulation in maize inbred Mp715. Molecular Breeding. 39:91. https://doi.org/10.1007/s11032-019-0997-0.
 Windham, G.L., Williams, W.P., Mylroie, J.E., Reid, C., Womack, E.D. 2018. A histological study of Aspergillus flavus colonization of wound inoculated maize kernels of resistant and susceptible maize hybrids in the field. Frontiers in Microbiology. 9:799. https://doi.org/10.3389/fmicb.2018.00799.
 Ogunola, O., Hawkins, L.K., Mylroie, J.E., Kolomiets, M., Borrego, E., Tang, J., Williams, W.P., Warburton, M.L. 2017. Genetic characterization of the maize lipoxygenase gene family in relation to aflatoxin accumuation resistance. PLoS ONE 12(7):e0181265.
 Coan, M., Senhorinho, H., Scapim, C., Pinto, R., Tessmann, D., Williams, W.P., Warburton, M.L. 2018. Genome-wide association study of resistance to ear rot by Fusarium verticillioides in a tropical field maize and popcorn core collection. Crop Science. 58:564-578. https://doi.org/10.2135/cropsci2017.05.0322.
 Varsani, S., Zhou, S., Koch, K.G., Williams, W.P., Heng-Moss, T., Sarath, G., Luthe, D., Jander, G., Louis, J. 2019. 12-Oxo-phytodienoic acid acts as a regulator of maize defense against corn leaf aphid. Plant Physiology. 179:1402-1415. https://doi.org/10.1104/pp.18.01472.
 Warburton, M.L., Womack, E.D., Tang, J.D., Thrash, A., Smith, J.S., Xu, W., Murray, S.C., Williams, W.P. 2017. Genome-wide association and metabolic pathway analysis of corn earworm resistance in maize. The Plant Genome. 11(1):170069. https://doi.org/10.3835/plantgenome2017.08.0069.