Evaluation of Hall’s Panicgrass (<i>Panicum hallii</i> Vasey) as a Model System for Genetic Modification of Recalcitrance in Switchgrass (<i>Panicum virgatum</i> (L.))

While switchgrass (Panicum virgatum (L.)) has long been recognized as a viable bioenergy feedstock, it and other plants have cell walls with recalcitrance to processing. Recalcitrance is recognized as a major barrier to broad adoption of switchgrass and other feedstocks for cellulosic bioenergy. In an effort to reduce recalcitrance, transgenic plants have been generated with altered cell wall phenotypes such as reduced lignin. Unfortunately, stable transformation of switchgrass and other C4 grasses is time intensive, costly, and genetic analysis is further complicated by polyploid genomic structures. Unlike switchgrass, which can be tetraploid to octoploid, a closely related species, Hall’s panicgrass (Panicum hallii Vasey), is diploid, and has a much smaller genome. In addition, Hall’s panicgrass is a smaller plant with a faster generation time and is capable of self-fertilization. In the present study, germplasm from two inbred populations of Hall’s panicgrass, FIL2 and HAL2, were selected to assess the feasibility of using Hall’s panicgrass as a model for switchgrass. Included in this work was the development of methods using seeds immediately harvested from plants grown in the greenhouse for germination, sterilization, callus induction, transformation, and regeneration. Seed germination was optimized on NB medium at 70 ±[plus or minus] 11% for FIL2 and 82 ±[plus or minus]3.0% for HAL2. Callus induction was optimized on MS-OG medium at 51 ±[plus or minus]29% and 81 ±[plus or minus]19% for HAL2. Shoot regeneration was optimized on REG medium at 11.5± [plus or minus] 0.8 shoots/gram for FIL2 and 11.3 ±[plus or minus]0.6 shoots/gram for HAL2. Root regeneration occurred at 100% frequency for all callus expressing roots on Diet-MSO. In addition to a complete tissue culture system, a suspension culture system was also developed to more rapidly produce tissue for cell-based experiments. Cell suspensions of Hall’s panicgrass, both FIL2 and HAL2, generated more callus after 16 weeks of culture (141 ±[plus or minus] 22% for FIL2; 302 ±[plus or minus] 54% for HAL2) than the solid-medium culture system.