Genetic Variability and Trait Relationships in Switchgrass

Greater knowledge of the magnitude of genetic variability for biomass yield and yield components in switchgrass, Panicum virgatum L., and relationships among the biomass yield component traits would facilitate the breeding improvement of the species. Accordingly, we conducted two replicated experiments to assess genetic variation for biomass yield and yield components and quantify relationships among those traits in different switchgrass populations. In Exp. 1, 228 half-sib families from SU C₃ and 261 from NU C₃ populations were evaluated at Perkins, OK, while 278 half-sib families from the SL C₀ population were evaluated at Stillwater, OK. Exp. 2 comprised 11 lowland switchgrass populations tested at Chickasha and Perkins, OK, in 1998. Substantial differences (P < 0.01) in biomass yield per plant existed among half-sib families within the respective SU C₃, NU C₃, and SL C₀ populations. Estimates of genetic variance for biomass yield were significant for each population. However, significant family × year and family × block variance estimates indicated substantial environmental influence in each of the populations. In Exp. 2, significant (P ≤ 0.05) variation existed among the 11 populations over locations for biomass yield per plant, tiller number per plant, tiller length, leaf blade length, and leaf blade width. Phenotypic correlation between biomass yield and tiller number per plant was positive (r = 0.68* at Chickasha and r = 0.60* at Perkins). Path coefficient analyses revealed that number of tillers per plant had the highest positive direct effect on biomass yield at both locations (0.74 at Chickasha and 0.66 at Perkins). Adequate genetic variability was present within the switchgrass populations to allow breeding improvement of biomass yield. Selection for increased number of tillers per plant would be the most effective means of indirectly increasing biomass yield.