Distribution of Wheat Head Blight, Identification and Characterization of Associated Fusarium Species in Southwestern Ethiopia

Abstract

Ethiopia is the second largest wheat (Triticum spp.) producer following Egypt in Africa. However, the crop is challenged by biotic, abiotic, technical and socio-economic constraints. Fusarium head blight (FHB) is one of the biotic factors caused by Fusarium species, which substantially reduces wheat grain yield and quality of the grain worldwide. This investigation was undertaken in order to assess occurrence and importance of FHB of wheat fields in southwestern Ethiopia (SWE), identify, characterize and test the pathogenicity of Fusarium spp. associated with FHB of wheat. Potential wheat growing zones, districts and peasant associations were selected by following purposive multi-stage sampling procedure. While, wheat fields were randomly assessed during early milk to hard dough stages and the disease severity was determined by the modified Horsfall-Barrett scale. Blighted heads were sampled and associated Fusarium spp. were isolated, identified and tested for pathogenicity on Danda’a variety. Results of this study revealed that FHB was 93.9 % prevalent in wheat fields with varying levels of incidence that ranged from 11.3 to 84.6 % in Buno-Bedele, 0 to 100 % in Jimma and 0 to 53.2 % in West-Wollega zone. FHB was high in Buno-Bedele with mean incidence of 38.7 % followed by Jimma (26 %), as opposed to 13.8 % in West-Wollega. Similarly, FHB was severe in Buno-Bedele having mean field severity, infected head severity and FHB index of 28.2 %, 33.2 % and 13.9 %, respectively. On the other hand, West-Wollega and Jimma zones had lower mean field severity of 12.8 % and 14.7 %, respectively. In addition, a total of 269 single conidial isolates of Fusarium was recovered from blighted head samples collected in 52 wheat fields. These isolates were identified into nine Fusarium species. Among them, F. graminearum (29.0 %) and F. culmorum (26.4 %) were the dominant species followed by F. avenaceum (10.4 %), F. poae (7.4 %), F. ussurianum (6.7 %), F. semitectum (6.3 %), F. lateritium (6.0 %), F. sambucinum (6.0 %) and F. heterosporum (1.9 %) in SWE. Pathogenicity tests revealed that isolates of Fusarium spp. caused symptoms of FHB in spikes of a susceptible Danda’a variety. Based on the spikelet infection severity and AUDPC results, F. avenaceum, F. poae, F. lateritium, F. culmorum, F. sambucinum, F. heterosporum and F. graminearum were more aggressive ones that produced higher AUDPC of 1067.2, 1066.3, 856.2, 801.3, 792.4, 670.9 and 546.8, respectively and higher spikelet infection severity of 57.8 % to 100 %. In conclusion, almost all wheat fields and all the wheat varieties grown in the study area were infected by FHB and also seven out of the nine identified Fusarium spp. were more aggressive, while the rest two showed less aggressiveness on Danda’a variety which was grown in most of the farmers field (50 %) in southwestern Ethiopia. These indicated that FHB of wheat will have a chance of becoming a potential disease in southwestern Ethiopia. Therefore, it needs surveillance, further phylogeny study of the causal agents and development of feasible management tactics in order to reduce the probable risk of FHB in southwestern Ethiopia and in Ethiopia at large.