Characterization of <i>Fusarium species</i> and <i>Alternaria alternata</i>, and their effects on switchgrass health and chemical components

Panicum virgatum L., readily referred to as Switchgrass, is a perennial warm-season bunch grass, used as an alternative energy source for biofuel production. There is insufficient research on switchgrass pathogens, and is expected that an increase in disease pressure will result as more land is reserved for this perennial crop. The purpose of this research was to identify and characterize pathogenic Alternaria alternata and Fusarium species on Switchgrass (Panicum virgatum L.), and to evaluate their impact on stand establishment and plant health. Molecular identifications of fungal isolates obtained from infected commercial switchgrass seed yielded eight species (A. alternata, F. acuminatum, F. armeniacum, F. equiseti, F. graminearum, F. oxysporum, F. tricinctum, and Phoma herbarum). Pathogenicity and virulence of identified isolates were determined with detached leaf assays. Except for F. oxysporum, all species were found to be pathogenic on the detached switchgrass leaves, with virulence varying between species and isolates within species. Fusarium graminearum isolates were the most virulent. Seed inoculation and whole plant inoculation assays were conducted to determine stand establishment and plant health. Overall, isolates of F. graminearum and F. armeniacum had the greatest impact on switchgrass stand and health and should be targeted for disease resistance development. Alternaria alternata isolates were found to be less virulent when compared to Fusarium isolates, only impacting moisture content of infected plants. Virulent isolate TBW107 was selected to determine the susceptibility of four switchgrass cultivars (‘Blade 1101’, ‘Blade 1102’, ‘Alamo’, and ‘Whippet’) to F. graminearum infection. ‘Blade 1102’ and ‘Alamo’ were found to be susceptible and ‘Whippet’ highly susceptible to F. graminearum infection. ‘Blade 1101’ was moderately resistant to F. graminearum infection and should be further studied to identify the source(s) responsible for resistance for cultivar development. The chemical analysis of switchgrass infected with virulent F. graminearum, F. armeniacum, and Bipolaris oryzae resulted in a significant increase in ash for B. oryzae infected biomass, and a decrease in carbohydrate content for B. oryzae and F. armeniacum infected biomass, reducing biomass fitness for biofuel conversion.