Distribution, Epidemics dynamics and physiological races of wheat stem rust (Puccinia graminisf.sp.triticiEriks and E. Henn) on irrigated wheat in the Awash River basin of Ethiopia

Abstract

Wheat is one of the high value important major crops of the globe. However, wheat stem rust is considered one of the determinant threats to wheat production in Ethiopia and the major producing areas of the globe. So this study was conducted with the following objective to assess the disease intensity, seasonal distribution dynamics pattern, the genetic variability of Puccinia graminis f. sp. Tritici and to determine its virulence spectrum in the irrigated ecology of Awash River basin. A total of 137 wheat farms were evaluated from 2014/15 - 2019/20 in six districts representing the Upper, Middle, and Lower Awash River basin. Farm plots were assessed every 5 - 10 km interval with 'X' fashion, and data on disease incidence, severity, and healthy plants were scored. Diseased wheat plant samples were collected for Puccinia graminis f. Sp. race analysis. The seasonal trend of wheat stem rust disease was also compared to infer the future potential production plan of irrigated wheat. The result revealed that the prevalence, incidence, and severity of stem rust were significantly varied among the different districts and seasons in the two regions. The survey results also indicated that about 71.7% of the wheat fields were affected by stem rust during the 2018/19 growing season. The overall incidence and mean severity of the disease during the same season were 49.02% and 29.27%, respectively. During 2019/20 about 63.7% of the wheat fields were affected by stem rust, which, however, the incidence (30.97%) and severity (17.22%) were lower than the previous season. Although the seasonal disease distribution was decreased, its spatial distribution was expanding in Afambo and Dubti. The physiological and the genetic race analysis identified four dominant races (TTTTF, TKTTF TKKTF, and TTKTF) during 2018/19 and one additional race (TKPTF) during 2019/20. The result indicated that the races are highly virulent and affect most of the Sr genes except Sr – 31 and Sr – 24. TTTTF and TKKTF are the widest virulence spectrum which affects 90% of the Sr genes. Thus, it can be concluded that the spatial and seasonal distribution of the disease is expanding. Moreover, most of the races were similar with rain-fed production, and thus care must be given for effective management of the diseases to both agro-ecologies. Therefore, these findings provide inputs for wheat producers to reduce the spread and damage of the disease in the irrigated ecologies of Ethiopia. Also, it gives an insight for breeders to think about the breeding program in their crossing lines.