Incidence of Seed-Borne Fungal Pathogens in Farm-Saved Common Bean (Phaseolus vulgaris L.) Seeds in Kagera Region, Tanzania

Common bean (Phaseolus vulgaris L.) is a vital source of protein and income for smallholder farmers in Tanzania. However, its productivity remains low, partly due to seed-borne diseases. This study assessed the incidence of seed-borne fungal pathogens in farm-saved bean seeds and examined their effects on common bean seed quality in Kagera Region, Tanzania. A total of 180 seed samples were collected from six villages across three major bean-producing districts. In Misenyi District, sampling was done in Kyaka Ward (Kyaka and Kashaba villages) and Nsunga Ward (Nsunga and Bulifani villages). In Karagwe District, seeds were obtained from Nyakasimbi Ward (Nyakasimbi and Bujara villages) and Ihanda Ward (Ihanda and Kandegesho villages). In Ngara District, samples were collected from Kirushya Ward (Kasange and Mwivuza villages) and Rusumo Ward (Mshikamano and Kasharazi villages). Standard seed health testing was conducted using the blotter method in accordance with ISTA guidelines to evaluate seed purity, moisture content, germination percentage, and fungal contamination. The experiment was laid out in a Completely Randomized Design (CRD) with three replications, and data were statistically analyzed using R software (R Core Team, 2024). Results revealed highly significant differences (p < 0.001) in fungal incidence across the sites. A strong negative correlation (r = –0.65) was observed between fungal infection and germination rate, seedling vigor, and overall seed quality. Among the pathogens identified, Colletotrichum dematium emerged as the most prevalent, with incidences of 4% in Ngara, 3% in Karagwe, and 0.5% in Misenyi. Contrary to expectations, Colletotrichum lindemuthianum (the causal agent of anthracnose) was not detected in any of the stored common bean seed samples. Fungal assays frequently yielded saprophytic isolates, including Aspergillus niger and Aspergillus flavus. Correlation analysis indicated that increased seed moisture content was significantly and positively associated with reduced seed viability (r = 0.49, p < 0.01). Furthermore, the level of fungal contamination showed a significant negative correlation with root development (r =−0.42, p < 0.01). These findings underscore the need to strengthen seed systems by promoting the use of certified seeds, improving post-harvest handling practices, ensuring proper drying and short-term, and encouraging the adoption of effective seed treatment protocols. Addressing these factors is crucial for reducing the transmission of seed-borne disease, improving seed quality, supporting sustainable bean production, and food security among smallholder farmers in Tanzania.