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Abstract
Switchgrass (Panicum virgatum, L.), a perennial warm-season grass, is a model herbaceous species for biofuel production and has been used for summer grazing to complement cool-season grasses. In this project, we mapped important traits that are related to seasonal growth and biomass quality. We mapped the genomic regions associated with winter dormancy level (measured through fall regrowth height, FRH and normalized difference vegetation index, NDVI), spring emergence (SE), flowering date (FD), and dry biomass weight. Phenotyping methodologies for winter dormancy, SE, and FD were initially tested in a switchgrass diversity panel consisting of 17 lowland, 5 intermediate, and 14 upland accessions. Using the ranges found in this study we were able to phenotype the traits in the two F1 populations derived from crosses between a non-winter dormant genotype B6 with the winter dormant genotypes AP13 (AB population) and VS16 (BV population). To perform QTL mapping, we constructed two linkage maps for each population using single nucleotide polymorphism (SNP) markers that were derived from genotyping by sequencing. A total of 2,772 and 3,766 SNPs were ordered in the AB and BV linkage maps, respectively, and we have successfully mapped 18 QTLs for FRH, 18 QTLs for NDVI, 21 QTLs for SE, 30 QTLs for FD, and 9 QTLs for biomass. In the second part of the study, we mapped 6 quality traits estimated by Near-Infrared Reflectance Spectroscopy (NIRS). These traits included Crude Protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Hemicellulose, Cellulose, and Klason Lignin. We found the ranges of cellulose (34.51 – 41.40%), hemicellulose (25.48 – 33.55 %), and Klason lignin (9.70 – 13.23%) to agree with other studies that determine these parameters in switchgrass. We identified 2 QTLs for CP, 9 QTLs for NDF, 8 QTLs for ADF, 9 QTLs for hemicellulose, 4 QTLs for cellulose, and 5 QTLs for lignin. The significant QTLs in this project are valuable marker resources to be used in our marker-assisted breeding selection. Markers found within the significant QTL intervals will warrant further in-depth validation of their usability in different genetic backgrounds.