IMPORTANCE AND INTEGRATED MANAGEMENT OF BACTERIAL BLIGHT (Xanthomonas campestris pv. sesami) OF SESAME (Sesamum indicum L.) IN NORTH GONDAR, ETHIOPIA

Abstract

Sesame is one of the important oil crops in Ethiopia for international market while its production is challenged by lack of appropriate agronomic practices, weather uncertainties, weeds, insects and diseases outbreaks. Bacterial leaf blight caused by Xanthomonas campestris pv. sesami is the most common and inflicts heavy qualitative and quantitative losses. The objectives of the present study were to assess bacterial blight incidence, severity and its association with agronomic practices; evaluate effect of chemical seed soaking agents against bacterial blight of sesame under laboratory conditions; and evaluate the effect of chemical seed soaking, host resistance and foliar spray on disease development, yield and yield components under field conditions. Field survey was conducted in Metema and Mierab Armachiho in 2014 cropping season at flowering and fruiting growth stages. A total of 80 fields were assessed for the disease assessment from both large and small scale farmers. Prevalence, incidence, severity and field management practices were recorded in each field. All surveyed fields were infected both at flowering and fruiting stage of the crop. Mean incidence over the two districts varied from 78% at Metema to 96.5% at Mirab armachiho. The minimum mean severity (6.1%) was recorded in Metema district and the highest mean severity (76.9%) was recorded at Mierab Armachiho. The association of independent variables with bacterial blight incidence and severity was varied. District, variety, growth stage, altitude, slope, crop density, previous crop, soil type and weed density variables were significantly associated with bacterial blight incidence. Variables producer and sowing date were non-significant as single predictor in the logistic regression model. Similarly, all the variables were significantly associated with bacterial blight severity. These variables are very important that influence bacterial blight epidemics. A laboratory experiment was done with factorial completely randomized design to evaluate six soaking agents on three varieties and untreated control at plant pathology laboratory Haramaya University. There were significant xvii differences among the soaking agents on seed germination (%), vigor index, sesame bacterial blight infection (%), and viability (cfu/ml). Maximum mean seed infection percentage (97%) was observed on untreated followed by distilled water (94%) and gentamicine sulphate (77%) treated units but the mean minimum seed infection percentage was observed on hot water (16%), and 1% sodium hypochlorite (24%) treated units. Soaking seeds with 1% sodium hypochlorite for thirty minutes or treating seeds with hot water at 52 oC for ten minutes lower the seeds infection percentage and viability of the bacteria. On this result 1% sodium hypochlorite and hot water treatments were selected for field experiment study. Field experiment was conducted at Metema experimental station on 2014 cropping season (from July to October) using three varieties, two soaking agents and foliar spray. Untreated seeds and unsprayed plots were left as control in each treatment. A total of 18 treatments were evaluated with randomized complete block design (RCBD) in a factorial arrangement with three replications. There was no interaction effect of variety with soaking combined with foliar spray except for disease progress rate. There were significant differences among the variety for incidence, severity, AUDPC, disease progress rate, seed yield and yield components. Interaction effect of varieties with soaking agents was observed for severity and AUDPC parameters. Variety Abasena and seeds treated with 1% sodium hypochlorite had lower intensity, AUDPC, progress rate of the disease and yield loss and high yield, net profit and marginal rate of return. Improved varieties, seed soaking agents and chemical application influence the level of disease epidemic and amount of yield loss attributed to blight of sesame.