Location: Corn Host Plant Resistance ResearchTitle: Quantitative Trait Loci for Resistance to Aspergillus Ear Rot: Analysis by Linkage Mapping, Characterization of Near-Isogenic Lines and Meta-Analysis) Author
Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2013
Publication Date: 1/1/2014
Citation: Mideros, S., Warburton, M.L., Jamann, T., Windham, G.L., Williams, W.P., Nelson, R. 2014. Quantitative trait loci influencing mycotoxin contamination of maize: analysis by linkage mapping, characterization of near-isogenic lines and meta-analysis. Crop Science. 54:127-142. Interpretive Summary: Most corn grown in the US is susceptible to the fungus A. flavus, which produces a substance called aflatoxin that is toxic to humans and most domesticated animals. Breeding corn plants that resist A. flavus and the buildup of aflatoxin is an effective method to solve the problem. Identification of chromosomal regions, called QTL, with large effects on resistance in different genetic backgrounds and environments, but which do not cover too large a piece of the chromosome, is necessary for improvement of this trait using Marker Assisted Selection (MAS). Several studies have identified QTL for resistance, and in this article, QTL from a new cross of resistant line CML322 x susceptible line B73 is presented. In addition, this article presents the results of a meta-analysis of A. flavus, aflatoxin, and ear rot resistance, using all available data sets in maize. Meta-analysis of QTL involves the use of multiple QTL mapping populations analyzed simultaneously to improve the power of identifying conserved QTL, and to reduce the genomic region it is found in. Some of the meta-QTL identified were further studied with Near Isogenic Lines (NILs) that compare corn plants with the metaQTL to corn plants that are genetically identical at all genes except that they lack the meta-QTL under study. One meta-QTL was validated in this way, and other regions containing meta-QTL further characterized (with mixed results). These results indicate that at least one meta-QTL, in bin 4.08 of the maize genome, should be effective in increasing resistance in all corn plants, wherever they are grown, and should be a top priority for MAS.
Technical Abstract: High levels of aflatoxin contamination of maize can be deadly for exposed human populations. Resistance to aflatoxin accumulation in maize has been reported in multiple studies and acts at multiple steps where there is fungal-plant interaction. In this study, we report the identification and mapping of quantitative trait loci (QTL) for multiple traits or components of resistance to A. flavus using different genetic tools and resources. For QTL mapping, we used the B73 x CML322 population of recombinant inbred lines from the nested association mapping genetic resource, and two mapping methods: a step-wise regression approach and composite interval mapping. Ten QTL were found using both QTL mapping methods, six of which were located to the same chromosome segments using both approaches. These QTL were located in maize bins 4.08, 4.09, 8.02, 8.03, 10.06 and 10.07. Various sources of near isogenic lines for selected loci were tested. The resistance QTL located in bin 4.08 was confirmed using a near isogenic line pair. Finally, we conducted a meta-analysis of QTL using data from 12 populations in which resistance to Aspergillus, Fusarium or Giberella ear rots has been mapped. The meta-analysis indicated that the QTL in bin 4.08 co-localized with QTL reported for three other mapping populations. Overall, we found evidence for significant QTL-by-year interactions and that QTL were distributed in an infinitesimal model. The largest effect QTL, located in bin 4.08, is a good candidate for further characterization of this trait.