Epidemics of Septoria Tritici Blotch and Its Development over Time on Bread Wheat in Haddiya-Kambata Area of Southern Ethiopia

Abstract

Bread wheat (Triticum aestivum L.) is one of the important cereal crops in Ethiopia. It is widely grown in most of the regions in the country, including Southern Nations Nationalities and Peoples Region (SNNPR); however its production is affected by abiotic and biotic factors. Among the biotic factors, Septoria tritici blotch (Septoria tritici) (STB) is one of the important problems of wheat production in the country; including Haddiya-Kambata areas of SNNPR. A field experiment was conducted at Hossana and Angecha in 2012 main cropping season to quantify the severity of Septoria tritici blotch and its rate of progression over time Three different spray intervals (10,20 and 30 days) of propiconazole (Tilt 250 EC) and one unsprayed plot for each of the three varieties (Alidoro, Galama and Gambo) were used to create different STB epidemic levels. Treatments were arranged in randomized complete block design (RCBD) with factorial arrangement in three replications. The epidemic of STB was developed at both locations. Severity on all leaves (i.e. the leaves except flag leaf) and on flag leaf was recorded independently at weekly intervals. Due to different number of scorings and inconsistence of growth stages of crop during STB assessment at both locations, Analysis was made separately for the two locations. At Hossana, maximum severity of 78% of STB was recorded on all leaves of the variety Gambo and 76% on Galama. At this location severity of 74% and 57% were recorded on flag leaf of Gambo and Galama, respectively. At Angecha, maximum severity of 59% and 33% were recorded on all and flag leaves of Gambo, respectively. Based on their coefficient of determination (R²), Gompertz model was best fitted than logistic for estimation of disease progression parameters. At Hossana on flag leaf, maximum progress rate of 0.074 gompit/day was calculated on unsprayed plot of Gambo and every 30-days sprayed plot of Galama and the progress rate of 0.058 gompit/day was calculated on all leaves of unsprayed plot of Gambo. The highest standardized AUDPC of 46.7%-day on flag leaf were calculated on unsprayed plots of Gambo at Hossana. The study showed that, STB disease epidemics was occurred at both locations. The highest level of severity and fast progress rate was recorded on unsprayed plots of all variety under the study with; including variety Alidoro that was previously reported as moderately resistant on other locations.  Moreover, level of severity and disease progress rate is affected by varieties and number of frequency of fungicide spray. On susceptible variety the disease reduced the grain yield was reduced from54qt/ha at controlled plot to 32.3 qt/ha on natural epidemic.

Keywords: wheat, Septoria tritice blotch, severity, progress rate, Area Under disease Progress Curve