Ecotypic and genotypic effects on regrowth and heading date in switchgrass ().

Switchgrass ( L.) is a native perennial grass species with great potential for bioenergy and forage. However, knowledge about its genetics and biology related to breeding is still in its infancy. Studying the diversity of switchgrass germplasm will shed light on variability, response to environmental conditions, adaptability, breeding, etc. Thirty-six switchgrass accessions/cultivars were used to study the ecotypic and genotypic effects on regrowth, heading date, and vegetative growth period. The R-360 honeycomb design was used for planting these accessions in 2007. Data on regrowth and heading dates were recorded in 2008, 2010, and 2011. Vegetative growth period was calculated by subtracting the regrowth date from the heading date. It was found that the lowland started regrowing earlier (77 ± 0.4 days of the year, DOY) than the upland ecotype (82 ± 0.3 DOY). The upland had earlier heading date (160 ± 0.4 DOY) than the lowland ecotype (173 ± 0.5 DOY). Vegetative growth period was about 18 days longer in the lowland (89 ± 0.6 days) than the upland ecotype (71 ± 0.4 days). For switchgrass (i.e., all accessions), biomass yield was related positively to growth period and heading date; however, biomass was only weakly related to regrowth. Therefore, when targeting biomass in the breeding program, growth period may be a quick and reliable reference in both ecotypes to quickly estimate biomass potential while regrowth and heading date may be better used as a parameter for accessions within an ecotype.