Location: Corn Host Plant Resistance Research
2018 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
More than 100 germplasm accessions from International Maize and Wheat Improvement Center (CIMMYT) are being screened in replicated field tests for resistance to fall armyworm leaf feeding this summer. A few of the accessions exhibited moderately high levels of resistance although not as high as the resistant checks that were developed by ARS at Mississippi State, Mississippi. Nevertheless, these newly identified resistant lines should be useful in ongoing efforts to produce corn hybrids with resistance to fall armyworm damage and other desirable agronomic traits. A bi-parental quantitative trait loci (QTL) mapping population of 250 segregating families that was genotyped by an industry partner was evaluated for leaf feeding damage in a replicated field trial this summer. Breeding crosses from the Germplasm Enhancement of Maize project (GEM) project are also being evaluated for resistance to fall armyworm damage Seed are being produced for a possible genome-wide association study (GWAS) of fall armyworm resistance. Two QTL mapping populations are also being evaluated for resistance to aflatoxin accumulation this summer. Data for two other populations that were evaluated in previous years is being analyzed and prepared for publication. Breeding lines selected for resistance to aflatoxin accumulation and resistance to fall armyworm and southwestern corn borer in previous years are being evaluated for those traits as well as other agronomic qualities. Test crosses of some of the most promising lines are being evaluated for yield. Gene expression in response to Aspergillus flavus infection and fall armyworm feeding is being compared on susceptible and resistant corn genotypes.
Accomplishments
