Effect of Cultivars and Temperature on Synergistic Interaction Between Panicum Mosaic Virus and Satellite Panicum Mosaic Virus in Switchgrass
Abstract Panicum mosaic virus (PMV), the type species of the genus Panicovirus in the family Tombusviridae, naturally infects switchgrass (Panicum virgatum L.). PMV and its molecular partner, satellite panicum mosaic virus (SPMV), interact synergistically in co-infected millets with exacerbated disease phenotype and increased accumulation of PMV, compared to plants infected only by PMV. In this study, we examined the reaction of switchgrass cvs. Summer and Kanlow to PMV and PMV+SPMV infections at 24°C and 32°C. Switchgrass cv. Summer was susceptible to PMV at both temperatures. In contrast, cv. Kanlow was tolerant to PMV at 24°C but not at 32°C, suggesting that Kanlow harbors temperature-sensitive resistance against PMV. At 24°C, PMV was readily detected in inoculated leaves but not in upper non-inoculated leaves of Kanlow, suggesting that resistance to PMV was likely mediated by abrogation of long-distance virus transport. Co-infection by PMV and SPMV at 24°C and 32°C in cv. Summer but not in Kanlow caused increased symptomatic systemic infection and mild disease synergism with slightly increased PMV accumulation compared to plants infected only by PMV. These data suggest that the interaction between PMV and SPMV in switchgrass is cultivar dependent, manifested in Summer but not in Kanlow. However, co-inoculation of cv. Kanlow by PMV+SPMV caused an enhanced asymptomatic infection, suggesting a role for SPMV in enhancing symptomless infection in a tolerant cultivar. These data suggest that enhanced asymptomatic infections in virus-tolerant switchgrass cultivar could serve as a source for virus spread and play an important role in panicum mosaic disease epidemiology under field conditions. Our data revealed that cultivars, co-infection with SPMV, and temperature influenced the severity of symptoms elicited by PMV in switchgrass.