Variation in fitness components can be linked in some cases to variation
of key traits. Metric traits that lie at the intersection of
development, defense, and ecological interactions may be expected to
experience strong environmental selection, informing our understanding
of evolutionary and ecological processes. Here, we use quantitative
genetic and population genomic methods to investigate disease dynamics
in hybrid and non-hybrid populations. We focus our investigation on
morphological and ecophysiological traits which inform our understanding
of physiology, growth, and defense against a pathogen. In particular, we
investigate stomata, microscopic pores on the surface of a leaf which
regulate gas exhange during photosynthesis and are sites of entry for
various plant pathogens. Stomatal patterning traits were highly
predictive of disease risk. Admixture mapping identified a polygenic
basis of disease resistance. Candidate genes for stomatal and disease
resistance map to the same genomic regions, and are experienceing
positive selection. Genes with functions for guard cell homeostasis, the
plant immune system, components of constitutive defenses, and growth
related transcription factors were identified. Our results indicate
positive selection is filtering genetic variance from one of the
parental species maladpated to a novel pathogen, and changing suites of
stomatal traits which contribute to disease variation in natural
populations.