Fusarium graminearum forms mycotoxin producing infection structures on wheat

The present investigation demonstrates the formation of foot structures and compound appressoria by F. graminearum. All infection structures developed from epiphytic runner hyphae. Compound appressoria including lobate appressoria and infection cushions were observed on inoculated caryopses, paleas, lemmas, and glumes of susceptible and resistant wheat cultivars. A specific trichothecene induction in infection structures was demonstrated by different imaging techniques. Interestingly, a ΔTRI5-GFP mutant formed the same infection structures and exhibited a similar symptom development compared to the wild type and the TRI5prom::GFP mutant.The different specialised infection structures of F. graminearum on wheat florets, as described in this study, indicate that the penetration strategy of this fungus is far more complex than postulated to date. We show that trichothecene biosynthesis is specifically induced in infection structures, but is neither necessary for their development nor for formation of primary symptoms on wheat.Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schwein) Petch) is the main causal agent of Fusarium head blight (FHB) disease of small grain cereals and cob rot of maize [1-3]. Mycotoxins produced by Fusarium species result in a loss of yield and reduced quality of grains [4-6]. Fusarium toxins including the trichothecenes nivalenol (NIV), deoxynivalenol (DON) and its derivatives 3- and 15-acetyldeoxynivalenol (3-ADON, 15-ADON) contaminate cereal products and have been shown to be harmful to humans, animals, and plants [4]. Hence, the European Union and the United States set limits for DON in final products for human consumption of 0.75 μg/g [Commission Regulation [EC] no. 1881/2006] and of 1 μg/g [Council for Agricultural Science and Technology, 2003]. Trichothecenes are potent phytotoxins for many plants. They can produce symptoms including wilting, chlorosis and necrosis at concentrations of 10-5 to 10-6 M [7]. The toxic effect of tri