Occurrence, Disease Co-existence and Preliminary Spatial Risk Indication of Common Bean Rust across Major Bean-Growing Zones of Tanzania

Common bean (Phaseolus vulgaris L.) is an important food and income crop in Tanzania, but its production is constrained by interacting fungal, bacterial and viral diseases. This study assessed common bean rust caused by Uromyces appendiculatus within the broader bean disease complex across major production zones. Evidence was obtained through a field survey, farmer questionnaire, targeted rust-confirmation sampling, research-centre plot assessments and exploratory spatial modelling. The field survey covered 433 bean fields and showed that angular leaf spot was the most frequently recorded disease (51.0%), followed by bean common mosaic virus (28.9%), anthracnose (23.3%), rust (21.9%) and common bacterial blight (20.8%). Rust occurrence differed significantly among production zones (χ² = 44.71, p < 0.001; Cramér’s V = 0.32), with the highest levels observed in the Western zone and Southern Highlands. Mixed infections occurred in 66.3% of rust-positive fields, most frequently involving angular leaf spot. Although chemical control was commonly reported by farmers, the use of resistant cultivars remained limited. Research-centre assessments similarly showed marked geographical variation, with the highest proportion of rust-positive plots and the greatest median rust incidence recorded at Uyole. Exploratory spatial models showed moderate-to-high apparent discrimination and were interpreted as preliminary surveillance-prioritisation tools. The findings demonstrate that common bean rust occurs within a geographically variable and multi-disease production environment. Strengthened field diagnosis, integrated disease surveillance, breeding for multiple-disease resistance and improved access to resistant varieties are therefore needed to support sustainable common bean production in Tanzania.