PT  - JOURNAL ARTICLE
AU  - Acer VanWallendael
AU  - Jason Bonnette
AU  - Thomas E. Juenger
AU  - Felix B. Fritschi
AU  - Philip A. Fay
AU  - Robert B. Mitchell
AU  - John Lloyd-Reilley
AU  - Francis M. Rouquette, Jr.
AU  - Gary Bergstrom
AU  - David Lowry
TI  - Geographic variation in the genetic basis of resistance to leaf rust in locally adapted ecotypes of the biofuel crop switchgrass (<em>Panicum virgatum</em>)
AID  - 10.1101/619148
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 619148
4099  - http://biorxiv.org/content/early/2019/04/26/619148.short
4100  - http://biorxiv.org/content/early/2019/04/26/619148.full
AB  - Pathogens play an important role in the evolution of plant populations, but genetic mechanisms underlying disease resistance may differ greatly between geographic areas as well as over time. Local adaptation is thought to be an important step in plant evolution, and may be impacted by differential pathogen pressures in concert with abiotic factors. This study uses locally adapted ecotypes of the native perennial switchgrass (Panicum virgatum) to examine the temporal and spatial variation in the genetic architecture of resistance to fungal pathogens, namely switchgrass leaf rust (Puccinia novopanici). To identify loci underlying variation in pathogen resistance in switchgrass, we scored rust damage across an outcrossed mapping population at eight locations across the central United States from southern Texas to Michigan. We followed rust progression at these sites for three years and mapped quantitative trait loci (QTLs) using function-valued transformations of rust progression curves. Overall, we mapped 51 QTLs that varied in presence and strength over the three-year period. Two large-effect QTLs were consistently associated with variation in rust progression in multiple sites and years, and are therefore potentially the result of the same underlying resistance genes. Interestingly, these two large-effect QTLs were almost exclusively detected in northern sites. This pattern could be caused by geographic difference in genetic architecture. The distribution of rust strains or variation in climatic conditions across the field sites could result in genotype-by-environment interactions in efficacy of rust resistance loci. Beyond reducing rust damage by 34%, the beneficial alleles at the two loci also increased biomass by 44%, suggesting a direct benefit by pleiotropy or indirect benefit through genetic linkage. Our results suggest an important role for fungal pathogens in the local adaptation of switchgrass and illustrate an influential geographic component of the genetic architecture of plant disease resistance.