Characterization of Candidate Overwintering Genes in Forage: Biofuel Napiergrass (Pennisetum purpureum Schumach.)

Sustainable bioenergy production and food security in the U.S. and globally must be compatible on a finite and limited land area. Perennial grasses are vital forage resources with recent interest in potential application towards renewable energy. Grasses with the highest rates of biomass accumulation are C₄tropical and subtropical species. Napiergrass (‘elephantgrass’; Pennisetum purpureum Schumach.; 2n=4x=28) is a tropical, C₄grass with superior forage quality and yield traditionally utilized as hay, silage, or grazing. Advances in biomass feedstock processing and conversion technology are facilitating development of lignocellulosic energy platforms. Perennial biomass feedstocks provide sustainable cropping system options via carbon sequestration, prevention of soil erosion, and mitigation of food security concerns by their utilization across marginal or abandoned lands. Similar to other high yielding dedicated energy crops such as sugarcane, napiergrass is adapted to the Southern United States (zone 8b). Applied and molecular genetic approaches are being utilized to select for biotypes adapted to climates that are more temperate. Current phenotypic selection for improved overwintering included several traits such as rhizome-derived shoots, rhizome distance from crown, and overall plant obustness. Initial screening was performed in Commerce, TX (zone 8a). Surviving genotypes were subjected to gene expression analyses using qPCR. A comparative genomics strategy that identified annotated genes with putative overwintering-related function and high synteny across grass species was utilized. For selected candidate genes, primer design was performed in Sorghum bicolor(L.) Moench., which is the most closely related species to napiergrass in the Panicoideae subfamily with a completely annotated genome. Rhizome tissue in the zones of cell division and elongation were analyzed separately, and tissue was collected for each adaptation zone in both the fall prior to winter dormancy and after overwintering during spring green-up.