Effects of loose smut on Digitaria sanguinalis population depending on seedling emergence period

Fungal plant pathogens can impact on host fitness. The effects of the systemic smut fungus Ustilago syntherismae on the morphology, growth and fecundity of the Digitaria sanguinalis population at the end of its annual cycle were assessed during two consecutive years considering the emergence time of host individuals (cohorts). U. syntherismae had an important impact on the D. sanguinalis population, because most of the infected plants (97.2%) were totally castrated. Smut fungus significantly reduced aboveground biomass (61.5%), height (23.7%) and the number of basal shoots (15.5%) and increased the number of nodes (12.9%), ramifications (52.4%) and inflorescences (16.7%) of the individuals. In view of the fact that the cohort was a significant source of variation in the percentage of diseased plants in the second year of study, our results do not support the idea that smutted plants appear earlier in the season, because the time of seedling emergence was not a factor that constrained the disease incidence.