Multi-Year Pathogen Survey of Biofuel Switchgrass Breeding Plots Reveals High Prevalence of Infections by Panicum mosaic virus and Its Satellite Virus.

Switchgrass (Panicum virgatum) cultivars are currently under development as lignocellulosic feedstock. Here we present a survey of three established switchgrass experimental nurseries in Nebraska in which we identified Panicum mosaic virus (PMV) as the most prevalent virus. In 2012, 72% of 139 symptomatic plants tested positive for PMV. Of the PMV-positive samples, 19% were coinfected with its satellite virus (SPMV). Less than 14% of all sampled plants in 2012 were positive for four additional viruses known to infect switchgrass. In 2013, randomized sampling of switchgrass individuals from the same 2012 breeding plots revealed that infection by PMV or PMV+SPMV was both more prevalent and associated with more severe symptoms in the cultivar Summer, and experimental lines with Summer parentage, than populations derived from the cultivar Kanlow. A 3-year analysis, from 2012 to 2014, showed that previously uninfected switchgrass plants acquire PMV or PMV+SPMV between harvest cycles. In contrast, some plants apparently did not maintain PMV infections at detectable levels from year-to-year. These findings suggest that PMV and SPMV should be considered important pathogens of switchgrass and serious potential threats to biofuel crop production efficiency.

Suppression of wheat Fusarium head blight by novel amphiphilic aminoglycoside fungicide K20.

K20 is a novel amphiphilic aminoglycoside capable of inhibiting many fungal species. K20's capabilities to inhibit Fusarium graminearum the causal agent wheat Fusarium head blight (FHB) and to this disease were examined. K20 inhibited the growth of F. graminearum (minimum inhibitory concentrations, 7.8-15.6 mg L-1) and exhibited synergistic activity when combined with triazole and strobilurin fungicides. Application of K20 up to 720 mg L-1 to wheat heads in the greenhouse showed no phytotoxic effects. Spraying wheat heads in the greenhouse with K20 alone at 360 mg L-1 lowered FHB severity below controls while combining K20 with half-label rates of Headline (pyraclostrobin) improved its disease control efficacy. In field trials, spraying K20 at 180 mg L-1 and 360 mg L-1 combined with half-label rates of Headline, Proline 480 SC (prothioconazole), Prosaro 421 SC (prothioconazole + tebuconazole), and Caramba (metconazole) reduced FHB indices synergistically. In addition, the K20 plus Proline 480 SC combination reduced levels of the mycotoxin deoxinivalenol by 75 % compared to the control. These data suggest that K20 may be useful as a fungicide against plant diseases such as FHB particularly when combined with commercial fungicides applied at below recommended rates.