The effects of smut (Ustilago destruens) on seed production, dormancy, and viability in fall panicum (Panicum dichotomiflorum)

Fall panicum (Panicum dichotomiflorum var. geniculatum), an abundant annual weed in southwestern Ontario, suffers large seed losses from the smut Ustilago destruens. From 19 to 83% of plants were infected in three sites surveyed. Some infected plants were completely sterile, but others produced small numbers of viable seeds. Most of these seeds did not give rise to smut-infected plants if they were not exposed to smut teliospores in the soil over winter. Compared with seeds from uninfected plants, those from infected plants had lower percent viability and weaker dormancy. When seeds from either infected or uninfected plants were mixed with smut teliospores over winter, 39% of the resulting plants were smut infected, compared with less than 1% of plants from seeds overwintered without smut teliospores. Seeds mixed with smut teliospores over winter did not lose viability, but some of them were slower to germinate the following spring. Key words: smut, fall panicum, seed viability, seed dormancy, germination, Ustilago destruens, Panicum dichotomiflorum.