Creating New Germplasm to Improve Aflatoxin Resistance in Maize

Maize (Zea mays L), the third largest crop produced in the world is susceptible to pre and post contamination of aflatoxin. Aflatoxin is a secondary carcinogenic metabolite produced by Aspergillus flavus, an opportunistic fungus of maize that causes ear-rot and subsequent production of aflatoxin. Host plant resistance is one of the promising long term solution to combat aflatoxin contamination in maize grains. Resistance to aflatoxin is heritable and resistant germplasms that can be used to reduce aflatoxin resistance has been developed. Creating quantitative trait loci (QTL) mapping populations to identify regions within maize chromosomes contributing to aflatoxin resistance help identify markers that can be used for successful introgression of the QTL into desirable backgrounds. To further confirm and validate QTL detected in a mapping population, creating near isogenic lines (NILs) with identified QTL is important. Furthermore, stacking of validated QTL through recurrent selection (RS) will help to improve aflatoxin resistance in maize. In this study, an F2:3 mapping population was derived from crossing CML69, an aflatoxin resistant inbred genotype unrelated to other genotypes used in previous mapping population and Va35, an aflatoxin susceptible inbred germplasm adapted to southeastern U.S. The F2:3 families were phenotyped for aflatoxin at Mississippi State, MS and Lubbock TX in 2016 and 2017 and genotyped using 1331 polymorphic markers. Composite interval mapping (CIM) identified 16 significant QTL in all four environments on chromosomes 1, 2, 3, 4, 5, and 7, and these QTL explains between 4% - 18% of the phenotypic variation observed in the population. Fourteen of the 15 QTL co-locate with previously identified QTL, suggesting that they will be stable in different genetic backgrounds and environments, and one novel QTL will provide additional resistance. Sixteen single nucleotide polymorphism (SNP) markers linked to QTL identified in a previous genome wide association mapping (GWAS) study were also used to create Near Isogenic Lines (NILs) to validate their effect on aflatoxin resistance. Finally, recurrent selection (RS) populations were created to increase the frequency of aflatoxin-resistant alleles from an 8-way cross derived from 8 aflatoxin resistant inbred maize lines

Characterization of Lipoxygenase (LOX) Gene Family and SNP Validation in Relation to Aflatoxin Resistance in Maize (Zea Mays L.)

An efficient approach to combat the accumulation of aflatoxin is the development of germplasm resistant to infection and spread of A. flavus in maize, one of the most important cereal grains in the world. Lipoxygenases (LOXs) are a group enzymes that catalyze oxygenation of polyunsaturated fatty acids (PUFAs). LOX derived oxilipins play critical roles in plant defense against pathogens such as A. flavus. The objectives of this study were to report sequence diversity and expression patterns for all LOX genes, and map their effect on aflatoxin accumulation via linkage and association mapping. Genes GRMZM2G102760 (ZmLOX 5) and GRMZM2G104843 (ZmLOX 8) fell under previously published QTL in one of four mapping populations and appear to have a measurable effect on the reduction of aflatoxin in maize grains. The association mapping result shows 19 of the total 215 SNPs found within the sequence of the ZmLOXs were associated with reduced aflatoxin levels