Leaf Spot Severity in Forage and Seed-Transmitted Exserohilum rostratum in Different Plant Phenological Stages

In order to obtain a successful pasture management, it is essential to know mainly the material to be sown, the local edaphic characteristics, and the disease epidemiology in these areas. Besides identifying the causal agent, the quantification of damage caused by pathogens is essential for the adoption of effective control measures. In this sense, seed transmission of fungi, which is the main transport mechanism in forage plants, is still little studied, as well as the severity and damage caused by the main diseases affecting plants. Thus, the objective of this work was to study the severity and progress of Exserohilum rostratum. The fungus was inoculated at different phenological stages of Brachiaria decumbens cv. Basilisk and Panicum maximum cv. Mombasa. The transmission of this pathogen from infected plants to seeds was also evaluated. The pathogen was inoculated in the plants at the following stages: Vegetative I; Vegetative II; Booting I; Booting II; Reproductive I; and Reproductive II. Severity was evaluated using a grade scale ranging from no symptoms to plants with more than 50% of affected leaf area. In order to evaluate the transmission of E. rostratum in seeds produced by the inoculated plants, the blotter test was used. E. rostratum was pathogenic to B. decumbens cv. Basilisk and P. maximum cv. Mombasa. Basilisk plants were susceptible in all phenological stages, with higher severity from the Vegetative II stage and greater progress between the second and tenth days after inoculation, coinciding with the seed-plant transmission of the fungal inoculum from this point on. For the cultivar Mombasa, higher severity of the disease during Vegetative stages I and II was observed, with the greatest progress of the disease between the second and fourth day after inoculation. Significant transmission of the inoculum from plants to seeds was observed from the Booting I stage.