Late Growth Stages of Johnsongrass Can Act as an Alternate Host of Colletotrichum sublineola

Twenty-six johnsongrass cultivars, collected from seven U.S. states, were spray inoculated with spores of an isolate of Colletotrichum sublineola derived from sorghum. Inoculations were made when plants reached growth stages of 2 (four to five leaves), 3 (seven to eight leaves), and 6 (post panicle emergence). At the earlier stages the johnsongrass cultivars showed hypersensitive responses and small lesions; however, acervulus formation was not observed. When late growth stage johnsongrass plants were spray inoculated, acervulus formation was confirmed in 19 cultivars as early as 5 days postinoculation. Results obtained confirm that johnsongrass can act as an alternate host of C. sublineola under favorable conditions, and growth stages of johnsongrass may be an important factor for cross infection of C. sublineola between johnsongrass and sorghum.