Distribution and association of faba bean gall (Olpidium viciae) disease with agro-ecological factors in northwestern Ethiopia

Faba bean (Vicia faba L.) is an important food legume crop used for various dishes due to its high protein and essential nutrients content. In recent years, faba bean production and productivity are constrained by faba bean gall (Olpidium viciae Kusano) disease in Ethiopia’s highlands. A total of 304 faba bean fields from 10 districts in three zones were surveyed during the 2019 and 2020 main cropping seasons to (1) assess the spatial distribution, prevalence, and intensity of faba bean gall disease and (2) determine its association with agro-ecological factors in northwestern Ethiopia. Weather data of each district were collected from meteorological stations and used for descriptive analysis. The gall disease prevalence (94.07%), incidence (43.41%), and severity (25.36%) were the highest in South Gondar. The gall disease was more severe in Tach Gayint (32.58%), followed in Lay Gayint and East Estie (25.34%) districts. The gall symptom was also observed on field pea, lentil, and vetch legume crops. The associations of faba bean gall disease intensity with agro-ecological factors were analyzed using the ordinal logistic regression model. Variables such as geographic area (zone), altitude, sowing date, and year were significantly associated with high disease incidence (> 50%) and severity (> 25%) in the model. Lower disease intensity had a strong association with intercropping, sowing from July to 15 August, good weed management, and altitudes below 2800 m. The gall disease epidemic was directly associated with high altitudes above 2800 m. High rainfall and humidity, leaf wetness, low temperature, and rain splash were identified as the most important driving for the gall disease epidemic and establishment in faba bean. Since a water-loving pathogen causes the gall disease, late sowing from July to 15 August, intercropping, good drainage, and growing faba bean below 2800 m should be considered as management options for the disease in faba bean production areas.