Infection of large crabgrass biotypes susceptible and resistant to an ALS-inhibiting herbicide by a smut fungus

Abstract

The widespread use of herbicides has contributed to the evolution of resistance in many weed species, including Digitaria sanguinalis (DIGSA), a grass important as weed that presents presents biotypes with different resistance mechanisms to acetolactate synthase (ALS)-inhibiting herbicides. Within the framework of eco-evolutionary dynamics in agroecosystems, it is important to pay attention to ecological interactions, such as those between plants and pathogens, since they could affect herbicide-resistant (R) and herbicide-susceptible (S) biotypes differently. One of these biotic interactions is the one established between DIGSA and Ustilago syntherismae, a fungus whose infection can prevent seed production in plants. An experiment has been carried out in which teliospores of the fungus have been placed in contact with seeds of R and S biotypes of DIGSA, applying a vacuum, in order to evaluate their infection by the fungus. The seeds were germinated in Petri dishes at 20°C 12h darkness / 30°C 12h light. After 10 days, the seedlings were cleared, stained and observed under an optical microscope to detect the systemic infection. The proportion of infected seedlings was subjected to statistical analysis. The results showed that the mean percentage of infection was significantly higher in the R biotype (98.4%) than in the S biotype (93.7%). Further studies are necessary to evaluate the possibility that herbicide resistance may have fitness costs in the plant-pathogen interaction.