Potential for Genetic Improvement of Resistance to Anthracnose in Switchgrass.

Anthracnose disease, caused by <i>Colletotrichum navitas</i>, is becoming more prevalent on switchgrass cultivars in the northeast USA.  Fourteen switchgrass cultivars were established in four locations in New Jersey (NJ) with three replications in a randomized complete block design in the spring of 2009. A switchgrass nursery consisting of 25 ecotypes with 12 plants per line was planted in a randomized complete block design with three replicates in the spring of 2008 at one location in NJ. Natural epidemics of anthracnose disease were observed in 2010 and 2013 in the cultivar trials and 2012 and 2013 in the nursery. Resistance was visually evaluated using a scale from 1-9, with 9 being the most resistant. Significant differences in levels of resistance were observed between cultivars and ecotypes. Overall, southern (SL) and northern lowland (NL) cultivars when grouped by type for analysis were consistently more  resistant to anthracnose disease when compared to northern (NU) and central upland (CU) cultivars across locations. However, when compared by individual cultivar, the CU cultivar, High Tide, was highly resistant at all cultivar trial locations. Timber (NL) exhibited the most consistent level of resistance along with SL ecotypes Performer, Bomaster and Alamo in these cultivar trials.  The upland ecotypes Blackwell (CU), Pathfinder (CU) Sunburst (NU) and KY1625 (CU) were the most susceptible across the different locations. Disease resistance assessed in 2012 and 2013 in the switchgrass nursery  also indicated stability of resistance of ecotypes across years. The cultivars High Tide, Timber and Alamo had high levels of resistance in 2012 and 2013; the most susceptible cultivars were Belgium, Falcon and Sunburst.  Blackwell and Pathfinder were also very susceptible in both years. The consistency of resistance across environments and years indicates that the resistance observed has a strong genetic component which indicates that breeding for resistance should be possible.