A simple culture method inducing sexual reproduction by Fusarium graminearum, the primary causal agent of Fusarium head blight

Authors: LU, SHUNWEN; EDWARDS, MICHAEL

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2018
Publication Date: 5/1/2018
Citation: Lu, S., Edwards, M.C. 2018. A simple culture method inducing sexual reproduction by Fusarium graminearum, the primary causal agent of Fusarium head blight. Plant Health Progress. 19:129-130. https://doi.org/10.1094/PHP-12-17-0079-BR.
DOI: https://doi.org/10.1094/PHP-12-17-0079-BR

Interpretive Summary: The fungus Fusarium graminearum is the primary causal agent of Fusarium head blight (FHB), a devastating disease of wheat and barley worldwide. This fungus can reproduce both asexually and sexually to make spores that infect host plants. The sexual spores (ascospores) are produced in fruiting bodies called perithecia that form on dead plant debris in nature. Currently, laboratory induction of sexual reproduction by the fungus requires special agar plates containing carrot extracts freshly made before use. The preparation of these carrot agar plates involves multiple steps, thus being time-consuming and inconvenient. This manuscript reports a simple method to induce sexual reproduction by the fungus that uses agar plates made from commercially available potato dextrose broth at a minimal cost (less $1 per liter) with one step preparation. Fungal sexual structures were induced on this type of plate by simply washing the growing mycelia on the plate with minimal medium solution without further treatments. Perithecia were produced just as well as with carrot agar plates. This method provides the FHB research community with an inexpensive, practical, and effective method to induce production of ascospores by this fungus.

Technical Abstract: The homothallic ascomycete fungus Fusarium graminearum is the primary causal agent of Fusarium head blight (FHB), a devastating disease of wheat and barley worldwide. The fungus undergoes both asexual and sexual stages in its life cycle. The asexual stage produces conidiospores, whereas the sexual stage produces ascospores. Both conidia and ascospores can initiate infection on the host, and the ascospore is an important primary inoculum of FHB. Induction of sexual stage of F. graminearum under laboratory conditions is important for molecular/genetic studies of the pathogen and FHB management, because the self-mating assays are essential for functional studies on mating-type and other homothallism-related genes. Induction of the sexual stage is also necessary for evaluation of the sexual reproduction potential of different isolates within the F. graminearum species complex, which affects disease epidemiology. The carrot agar method currently used as a standard protocol for this purpose is inconvenient and time-consuming because it involves multiple steps in preparation. Here we report a simple culture method for the same purpose. In this method, the fungus was first inoculated onto a quarter-strength potato dextrose agar (PDA) plate containing 6 g/per liter of potato dextrose broth, and the fungal mycelia/macroconidia were simply washed from the plate with 5 ml of minimal medium solution after incubation for seven days. Following continued incubation about 12 days, dark black fruiting bodies (perithecia) were formed abundantly on the PDA plate with the average number per plate comparable to those obtained from the carrot agar procedure. Microscopic examination confirmed that >90% of perithecia formed on the PDA plate were fertile with Gibberella zeae-type asci and ascospores.