Characterizing Switchgrass (Panicum virgatum L.) Cytotypes.

Switchgrass (Panicum virgatum L.) is a warm season C₄ perennial grass and was chosen as a model bioenergy feedstock species by the Department of Energy. Switchgrass populations are classified into two distinct cytotypes (upland and lowland) which are adapted to distinct geographic locations in the USA. These cytotypes also differ with respect to photosynthesis, stress tolerance and nutrient use efficiency. The objective of this study was to evaluate these cytotypes for phenotypic variability, molecular marker diversity and response to micro-propagation using nodal culture. Eight genotypes each from three lowland (Alamo, Kanlow and Grenville) and three upland (Summer, Shawnee and Blackwell) cytotype populations are being evaluated in a field trial at the Research Station in Ardmore, OK for estimation of different growth habit, disease resistance, and morphological and biomass related traits.  Lowland cytotypes are found to be larger and more robust than their upland counterparts. Genotypes of lowland cytotypes are generally more tolerant to stem rust (Puccinia emaculata) than the upland accessions. Populations are being characterized using EST-SSR (expressed sequence tag - simple sequence repeat) and genomic SSR markers to assess the allelic variation. A higher marker variation amongst the lowland genotypes was evident. In-vitro propagation ability using nodal culture indicated that the upland cytotypes have shown higher propagation ability compared to lowland cytotypes. Detailed morphological, marker and nodal-propagation variability among switchgrass cytotypes will be discussed.