The Role of Setophoma terrestris in Pink Root Disease: New Insights and Host Range in Brazil

The soil-borne fungi, <i>Setophoma terrestris</i> and <i>Fusarium</i> spp., are often associated with pink root, although the etiology of the disease remains doubtful. While recognized as the primary inoculum, studies show conflicting views on the formation of chlamydospores and microsclerotia in <i>Setophoma</i>. Therefore, this study aims to clarify the etiology of the pink root of garlic and onion and the formation of chlamydospores and microsclerotia in <i>Setophoma</i>. The isolates were obtained from symptomatic tissues of garlic, leeks, brachiaria, onions, chives, and maize collected from seven different states in Brazil. Representative isolates were selected for pathogenicity tests. Sequence comparison of the tubulin gene showed <i>Setophoma</i> (<i>n</i> = 50) and <i>Fusarium</i> clades (<i>n</i> = 25). Garlic and onion plants inoculated with <i>Setophoma</i> showed pink root symptoms, while plants inoculated with different <i>Fusarium</i> isolates remained asymptomatic. Multigene analysis of pathogenic isolates confirms that only <i>Setophoma terrestris</i> causes pink root in garlic and onion. In addition, brachiaria, chives, and leeks are newly identified hosts of this pathogen in Brazil. To our knowledge, the main sources of primary inoculum of the disease are chlamydospores, pycnidia, colonized roots of garlic, onion, and plant debris of susceptible crops. The new information obtained in this study will be fundamental for researchers in the development of genotypes that are resistant to pink root and will help the efficient management of the disease.