DISTRIBUTION, MYCOTOXIN DETERMINATION AND MANAGEMENT OF BREAD WHEAT (Triticum aestivum L.) FUSARIUM HEAD BLIGHT IN ETHIOPIA

Abstract

Wheat is among the most important cereal crops produced in Ethiopia and is cultivated over large area. However, it's production and productivity are affected by biotic and abiotic constraints, mainly fungal diseases leading to in limiting production. Among these, Fusarium head blight (FHB), caused by multiple Fusarium species, is one of the most important diseases that cause noteworthy yield and quality losses due to toxin accumulation. Thus, the present study was carried out to achieve the following objectives: 1) determine the prevalence and intensity of wheat FHB in major wheat-growing areas of Ethiopia, and its association with biophysical factors; 2) determine the major fungal species and levels of multiple-mycotoxins in wheat grain samples collected from farmers fields; 3) assess the effect of wheat variety resistance and fungicide application on FHB and deoxynivalenol (DON) contamination, and evaluate differences in wheat variety reaction to FHB and DON contamination; and 4) evaluate wheat varieties' responses to spray inoculation with F. graminearum mixture. The study consisted of survey, laboratory greenhouse, and field work activities. A total of 264 wheat fields in 12 districts were assessed in 2020 and 2021main cropping seasons. The associations of FHB intensity with independent variables were analyzed using a logistic regression model. In addition, multi mycotoxins analysis was carried out using liquid chromatography-tandem mass spectrometric (LC-MS/MS) to dertermine levels of multiple-mycotoxins in wheat grain samples. A greenhouse experiment was conducted to evaluate the responses of wheat varieties to spray inoculation with F. graminearum mixture. Furthermore, field experiments were conducted in Mareko district, during the 2020 and 2021 main cropping seasons to determine the impact of integrated wheat variety resistance and fungicide application against FHB development and DON contaminations. The treatments were arranged in randomized complete block design with three replications. Survey results indicated that 93.56% of wheat fields were infected with FHB disease. Disease intensity varied among district, year, altitude, preceding year crop, crop growth stage, weed status and tillage practice. The mean disease incidence in the two years ranged from 22.28 to 53.35%, while the disease severity index ranged from 16.57 to 37.73% in the Limuna Bilbilo and Mareko districts, xv respectively. High disease incidence (> 37%) and severity (> 28%) was significantly associated with Mareko district, maize as a previous crop, high weed infestation and minimum tillage. Lower disease incidence (≤ 37%) and severity (≤ 28%) had a high probability of association with the Limuna Bilbilo district, adequate weed management, maximum tillage, and wheat field rotation with legume crops. Mycological analysis revealed that wheat grain samples were infected with various fungal genera of Alternaria, Aspergillus, Fusarium, Penicillium, and Rhizopus species, of which Fusarium species were abundantly prevalent. The results of the multi-mycotoxin analysis revealed that 49 metabolites from different fungal species, including masked, regulated, and emerging mycotoxins, were detected and grouped into eight categories. Among major mycotoxins and derivatives, DON was frequently detected in 70.8% of samples with the maximum concentration 15900 µg/kg, followed by its masked metabolite of DON-3-glucoside detected in 64% of the samples with maximum level of 2120 µg/kg. The integrated management experiment showed variation among treatments. Kingbird variety sprayed with tebuconazole had low mean FHB disease severity of 19.33 and 20.20%, disease progression of 0.0065 and 0.0079units day-1 and AUDPC of 316.52 and 330.17%-days in 2020 and 2021, respectively. With reference to yield performace, high mean grain yields of 6.55 t ha−1 (2020) and 5.40 t ha−1 (2021) were also obtained from Kingbird variety sprayed with tebuconazole. Furthermore, fungicide efficacy against mycotoxin contamination control was found to be higher in the Kingbird variety treated with tebuconazole, with 67% DON levels reduction than the control plots. The evaluated traits were significantly interrelated and showed very high variation at P ≤ 0.0001 among wheat varieties. The disease progression rate of the Kingbird variety inoculated with F. graminearum was low (0.0191 units day-1 ), whereas Ogolcho had the highest and fastest disease progression rate (0.0581 units day-1 ). Disease severity index among the varieties varied from 29-72%, while AUDPC varied from 326-1010%-days. Wane, Kingbird, and Limu were moderately resistant, with lower disease severity, AUDPC, and a reduction in thousand grain weight and grain weight per spike. The research results imply that integrating fungicide application with moderately resistant varieties is a more effective and better management approach for reducing FHB and DON contamination in wheat while enhancing wheat productivity and food security in Ethiopia's major wheat growing areas.