A New Threat to Switchgrass: Anthracnose Leaf and Stem Blight.

Panicum virgatum (switchgrass) is a warm-season perennial grass which has recently gained fame as a renewable, plant-based bioenergy source.  Breeding for high-yielding switchgrass cultivars has resulted in the establishment of extensive monocultures that may fall victim to disease epidemics if potential disease threats are not considered during the breeding process.  Because switchgrass is a native plant, disease threats have been predicted to be minimal for this crop; however, switchgrass stands in Pennsylvania, New York and New Jersey have recently exhibited symptoms of anthracnose disease, contradicting this theory.  In this study, we set out to determine the identity of the fungus responsible for anthracnose disease symptoms in switchgrass.  Morphological data, multilocus DNA sequencing and phylogenetic analysis identified this pathogen as a novel species within the genus Colletotrichum.  Growth chamber experiments fulfilled Koch’s postulates and provided the first experimental evidence that Colletotrichum is responsible for anthracnose disease of switchgrass. Our data show that this anthracnose disease is caused by a novel species of Colletotrichum, which we formally describe as C. navitas (navitas = Latin for energy). These findings suggest that pathogens may pose a significant threat to cultivated switchgrass despite its indigenous past, and that ongoing research is needed to determine the effects of C. navitas on commercially grown switchgrass cultivars in the field.  The data generated from these experiments will be utilized to determine the importance of assessing anthracnose disease resistance during the breeding process.