An industry perspective on whole genome-informed hybrid maize disease resistance characterization to improve breeding decisions

Characterizing hybrid maize disease resistance is a costly and labor-intensive effort in commercial breeding programs. Field trials are carefully inoculated and managed but remain error-prone due to spatial variability in disease pressure, microclimatic conditions and inter-rater variability. Quantitative ordinal disease rating scales are used to increase scoring speed at the expense of resolution, accuracy, and the ability to use conventional statistical methods. To improve traditional methods of disease resistance characterization, we propose to leverage readily available low-density SNP marker profiles to create genome-informed disease scores. Specifically, a whole genome ordered probit regression (WGOPR) model is used to deconstruct field-observed disease phenotypes into marker effects and reconstruct genome-informed disease scores. This approach is demonstrated in hybrid maize using data from Exserohilum turcicum-inoculated field trials across the central and northern U.S. and Canadian Corn Belt in 2024. Resulting Genomic Estimated Categorical Probabilities (GECPs) are compared to observed frequencies of disease scores to validate the methodology and evaluate the accuracy of regional hybrid maize disease resistance characterization. The benefit of a probabilistic output is demonstrated through two use cases: a comparison of hybrids with highly variable observed disease resistance scores at a single location, and a comparison of breeding selection schemes from a regional analysis. Because GECPs are the product of estimated marker effects, they better represent the expected behavior of a genotype independent of location-, rater- and plot-specific noise, and will therefore offer a step towards improving hybrid maize characterization and better informing breeding decisions.