Multitrait Association Mapping: Analysis of Quantitative Resistance to Maize Diseases.

Plants are attacked by pathogens representing diverse taxonomic groups, such that genes providing multiple disease resistance (MDR) would likely be under positive selection pressure.  We examined the hypothesis that there is a pleiotropic genetic basis for MDR in maize in the context of naturally occurring genetic variation.  To do so, we extended coancestry-controlled genetic association mapping to a multivariate statistical framework to allow multiple traits to be examined together.  Moderately high positive genetic correlations were found between resistances to three different diseases measured in a public panel of diverse maize inbred lines.  Linkage disequilibrium among these inbred lines generally decays over very short physical distances (sometimes within genes), suggesting that functional allelic variation at specific genes or tightly linked loci for MDR exists in maize.  We also used the multivariate model to test multitrait-marker associations, and glutathione S-transferase was identified as a putative MDR gene.  The gene’s documented general role in cytoprotection, including defense against pathogen infection, provided biological plausibility for the association in terms of shared aspects of pathogenesis for the pathogens studied.  Glutathione S-transferases and genes involved detoxification pathways are potentially an important component of functional variation in quantitative disease resistance.