Significant Marker-Trait Associations for Heading Date, Anthesis, Greenup, and Cell Wall Properties in Upland, Lowland, and Hybrid Populations of Switchgrass

Switchgrass (Panicum virgatum L.) is a high-yielding, perennial C4 grass that is currently being improved for use as a bioenergy feedstock. Populations being developed for the Upper Midwest growing region include hybrids derived from cultivars 'Summer and 'Kanlow' that are of upland and lowland ecotypes respectively . We have conducted a genome wide association study on breeding material that represents subselections of these cultivars and their hybrids with the aim of identifying markers associated with increased cell wall digestibility, early spring growth and late maturity. Five subselections comprising 125 different genotypes each were clonally propagated in a randomized complete block design with three replicates. The plants were established in 2011 and phenotyped in 2012 and 2013 growing seasons for dates of heading, anthesis, and initial growth, as well as dry matter yield and cell wall properties estimated by near infrared spectroscopy. The populations were genotyped by sequencing of reduced representation libraries created from gDNA digested with PstI. After imputation of missing data a mixed model controlling for population structure and kinship (PxK) was used to identify significant marker trait associations and control the type I error rate. Several genomic regions were significantly associated with heading date, and greenup, as well as some cell wall properties. However, no significant interactions were detected for yield.