Genetic variation for Puccinia emaculata infection in switchgrass

Seed yields, forage quality, and biomass of switchgrass (Panicum virgatum L.) can be negatively impacted by diseases. Genetic vulnerability is a concern when one switchgrass cultivar is grown in monoculture for long periods of time. Thus, genetic variation is key to improvement in pest resistance through selection. Our objectives were to develop a rust rating system for Puccinia emaculata Schwein and to determine genetic variation for P. emaculata infection among and within four improved switchgrass populations from the northern and central Great Plains. Populations were evaluated in replicated family-row nurseries at two locations (Aurora and Kimball) in eastern South Dakota. Disease ratings were taken after heading in 2000 and 2001 utilizing a 0 (highly resistant) to 9 (highly susceptible) scale. Population mean rust ratings averaged across families and years ranged from 3.7 to 8.0, and 3.2 to 5.0, at Aurora and Kimball, respectively. Significant variation among populations and among and within families within populations was observed for disease ratings. Data suggested the presence of both additive and nonadditive genetic variation and indicated selecting the best individuals from the best families for resistance to the rust disease may be an effective approach in utilizing genetic variation for improvement in switchgrass for the northern and central Great Plains.