Characterization of cereal Fusarium species resistant to major seed disinfection fungicides

Abstract

Fusarium species are known to be major producers of mycotoxins, causing Fusarium head blight (FHB) disease, which reduces wheat yield and quality. To complete this study, 60 samples of durum wheat with symptoms of the disease, belonging to six varieties, were collected randomly from seven provinces in northeastern Algeria during the years 2017 and 2018 to determine the pathogens prevalence and their importance, the association of the pathogens with nutritional and climatic factors, as well as the effectiveness of fungicides to their control. Eighteen fungal isolates were isolated and then identified as belonging to seven different species of Fusarium, namely F. clavum, F. culmorum, F. microconidium, F. avenaceum, F. tricinctum, F. solani, and F. acuminatum using polyphasic analysis. The results showed that F. clavum was the most abundant, found in 33.3% of the samples. This study also indicates the presence of F. clavum, F. microconidium, and F. tricinctum, for the first time in durum wheat ears in Algeria, and F. microconidium in durum wheat worldwide. The pathogenicity of isolates on three durum wheat cultivars (GTAdur, Cirta, and Waha) was evaluated using in vivo and in vitro tests, which showed a significant difference between isolates and between species, with F. avenaceum (FusBi7) being the most aggressive, and Cirta variety as the most tolerant. Regarding mycotoxins production, all isolates tested were able to produce deoxynivalenol (DON), zearalenone (ZEA), and T-2 toxin (T-2), with the distinction of F. culmorum (FusBo59) as being the most productive. In addition, the results showed that the DON is the most abundant with 7.128 μg.kg-1 recorded by ELISA and 373196.19 μg.kg-1 by LC-MS/MS, exceeding the European Commission limits (1750 μg.kg1). On the other hand, the analysis of the toxins presents in the durum wheat samples revealed that 15-ADON was more present (63.6%) than DON (18.2%) and 3-ADON (9.1%). The study also showed that physical and chemical factors, as well as nutritional factors, greatly affect the growth ability of the isolates. Laboratory studies using a one-factor method at a time to understand the physiological aspect of Fusarium isolates indicated that Czapek Dox Agar, at 25°C, 95% relative humidity, pH 7, 2.5 g. L-1 of salinity, cellulose as a carbon source, peptone as a nitrogen source and a 10:1 ratio of C:N, recorded optimal fungal growth for the Fusarium isolates. Antifungal activity assays also demonstrated that the fungicide tebuconazole (Raxil and Tebuzol) and the combination of fludioxonil + difenoconazole significantly inhibited the fungal growth of the isolates by 84.31%, 82.94%, and 81.33%, respectively, compared to difenoconazole alone (73.16%) at the recommended dose after five days of exposure. Tebuconazole (Tebuzol 73.46%, Raxil 69.75%) had a greater effect on spore germination than fludioxonil + difenoconazole (62.16%) at the recommended dose leading to conidial deformation and fragmentation. Keywords: Epidemiology, wheat, Fusarium spp., mycotoxins, fungicides.