Geographical Distribution of Fusarium Species Involved in Fusarium Head Blight and Fusarium Crown Rot of Wheat in Tunisia and Their Mycotoxin Accumulation

Fusarium crown rot (FCR) and Fusarium head blight (FHB) are among the most destructive diseases of wheat worldwide. A broad range of Fusarium species is associated with both diseases and can be isolated from stems and kernels of wheat plants. Fusarium culmorum and F. graminearum are the most frequent species involved, and both can produce the harmful mycotoxin deoxynivalenol (DON) that inhibits protein synthesis. This study aimed to assess the distribution of both Fusarium species and DON accumulation in crowns and kernels in geographic areas where wheat is cultivated in Tunisia. Sixty-four fields from four bioclimatic zones were sampled during two crop seasons (2020/2021, 2021/2022). Based on morphological traits, a subset of 250 representative Fusarium strains was identified by elongation factor 1α gene sequencing. DON contamination in wheat samples was determined by HPLC/DAD. Chemical analyses showed that DON contamination in crowns ranged from around 0.1 to 17 mg kg−1, while in kernels it was detected at a very low level (up to 2.4 mg kg−1). F. culmorum was the species frequently isolated from both crown and kernel samples. However, several Fusarium species, belonging to eight different phylogenetic species complexes, were isolated, showing a greater diversity in the crown than in the kernels. We report here for the first time the occurrence of F. anthophilum, F. nygamai, F. algeriense, F. redolens and F. brachygibbosum in Tunisian wheat. Moreover, this study provides important information on the toxicological risk related to DON contamination of wheat in Tunisia.