Biological Systems Engineering


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor Gary Y. Yuen. Lincoln, Nebraska: August, 2014

Copyright (c) 2014 Catherine Louise Stewart


New switchgrass (Panicum virgatum L.) cultivars are being developed for use as a biofuel pyrolysis feedstock. Viral pathogens have been reported in switchgrass, but their importance in biofuel cultivars is not well known. In 2012 surveys of five switchgrass breeding nurseries in Nebraska, plants with mottling and stunting— symptoms associated with virus infection—had an incidence of symptomatic plants within fields as high as 59%. Leaves from 120 symptomatic plants were analyzed by ELISA for Panicum mosaic virus (PMV) and four other viruses known to infect switchgrass. Most samples (87%) were positive for PMV, and fewer than 8% for the remaining viruses. Among PMV-positive samples, 36% tested positive for the presence of PMV’s satellite virus (SPMV) by immunoblotting.

In 2013 fields were assessed for PMV- and PMV+SPMV-infection incidence and associated symptoms. PMV and SPMV were detected by ELISA and RT-PCR, respectively, in leaf samples from randomly selected plants. Symptom severity was assessed on these plants using a 1 to 5 scale (1 = no symptoms; 5 = plants stunted and >50% foliage with mottling). PMV incidence varied among fields and switchgrass populations within fields. Common among sampled populations was dual infection by PMV and SPMV. Few plants were infected with PMV alone and these exhibited symptoms at the 1-3 rating. There also were many PMV+SPMV-infected plants and these exhibited symptoms at the 1 to 5 rating.

To assess potential resistant switchgrass, four strains of switchgrass were grown in a growth chamber and rub-inoculated with PMV and PMV+SPMV. These were observed for 30 dpi and then collected. During the 30 dpi there was little symptom expression. Samples were weighed and tested for the presence of PMV or SPMV via RT-PCR. This study is on-going; however presently there is no evidence of resistance to either PMV or PMV+SPMV infection. However, the four switchgrass strains had less biomass accumulation if infected with either PMV or PMV+SPMV. There was no significant difference in biomass accumulation between PMV and PMV+SPMV infection.

Adviser: Gary Y. Yuen