Biomass yield reductions in switchgrass due to smut caused by Tilletia maclaganii.

Switchgrass (Panicum virgatum) is an attractive biomass crop for renewable energy, but there is little information on disease losses. Tilletia maclaganii causes a smut disease of switchgrass that results in stunting, premature flowering, and replacement of seeds by fungal sori. We conducted a study in naturally-infested fields to describe the impact of smut on biomass yield. Ten fields were sampled; smut incidence, stand density, and biomass yield were determined. Disease incidence varied from 0.7 to 55.4% (26% overall) and biomass varied from 174 to 617 g/m². Mean biomass/tiller was significantly reduced by the disease in each field, by 38 to 82%. Yield loss was calculated based on the ratio of mean biomass/tiller for samples (actual yield) and mean biomass/tiller for healthy tillers (attainable yield). Yield loss estimates ranged from 1.7 to 40.1% among the fields. There was a strongly linear relationship (R² = 0.95) between disease incidence and yield loss, and regression analysis estimated a 0.66% reduction in yield for every 1% increase in disease incidence. According to this model, yield loss for all sampled fields was estimated at 17.0%. This disease is having a significant impact on biomass production in Iowa, and there is a critical need for research on management approaches if switchgrass is to be successful as a feedstock for lignocellulosic ethanol production.