Functional Disease Phenotyping Partitions Field Protection into Host Genetic Resistance and Phenological Escape in Wheat Head Blast

Wheat head blast can cause severe yield losses in Brazil’s Cerrado, a key region for expanding wheat production. Field phenotyping is essential for characterizing host resistance, but phenological differences among them, such as heading time, can confound these assessments by altering exposure to weather that influences disease development. We developed an analytical framework to partition and quantify the contributions of host resistance and phenological escape to disease protection and to further classify wheat genotypes according to wheat blast resistance. We tested the proposed approach using head blast incidence data collected over time for 20 cultivars evaluated across 16 field environments, conducted from 2018 to 2025. We used estimates of heading dates relative to BRS 264 cultivar, an early-maturing and highly susceptible standard, to quantify weather-based risk around heading. We fitted a hierarchical generalized additive model and integrated differences among predicted incidence progress curves over 30 days after heading to derive indices of cultivar resistance under standardized weather-based risk, phenological escape, and overall protection relative to BRS 264. Nested Monte Carlo simulations propagated uncertainty in the weather-based linear predictor and disease progress model coefficients to these indices. Mean escape estimates varied little across heading-date scenarios for most cultivars. Cultivar resistance generally contributed more than phenological escape to reductions in predicted incidence. Clustering disease progress curves predicted under standardized weather-based risk identified susceptible and moderately resistant groups. Even small contributions from phenological escape could affect field assessments of cultivar resistance, underscoring the importance of accounting for weather exposure at crop heading.