The phenotype of any plant can be broken down into the three primary sources of variation, genetic (G), environment (E), and genetic by environmental interaction (GxE). Producers and researchers alike will harness repeatable G and GxE effects to maximize their resource efficiency. This study studied the G and GxE effects in the biotic stress of the fungi Phyllachora maydis and the environment patterns in advanced yield trial data. In rating 800 genotypes over two seasons, we genetically mapped and identified over 100 significant Single Nucleotide Polymorphisms (SNPs) associated with tar spot resistance using a genome-wide association study. We then conducted genomic prediction, which was 81.5% accurate for predicting tar spot severity within the location and 48% accurate in predicting disease resistance in a new environment. Also, using Genetic and Genotype x Environment (GGE) biplots, we investigated environmental patterns of nine locations in three maturity Zones in the advanced yield trials in the Michigan Yield Performance Trials. First, we identified two locations, one in the late and one in the mid maturity zone, with equal G and GxE effects and should be removed. Then, using a sliding window of year combinations, we analyzed the optimal number of replications needed across the three maturity zones. We determined that an average of three replications are needed to achieve 75% of the maximum repeatability across the zones.
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