Incidence of Cercospora Leaf Spot on Soybean (Glycine max) in Borno State, North East Nigeria

Soybean (Glycine max) production in Borno State has gained momentum in recent years as farmers seek drought-tolerant and nutritious crop alternatives in the North East. However, the spread of Cercospora leaf spot disease, caused by Cercospora sojina, has been identified as an emerging threat to productivity in this region. This undergraduate investigation documented the incidence of Cercospora leaf spot on soybean across four local government areas in Borno State during the 2023 rainy season. Field surveys were conducted fortnightly from planting to maturity, with disease incidence and area under disease progress curve values computed for each location. Fungal isolates from affected leaflets were characterised morphologically and cross-referenced with published keys. C. sojina was confirmed as the predominant pathogen, with occasional co-infections by Alternaria species noted. Disease incidence peaked at mid-pod-fill stage, averaging 49 percent across all sites. Fields with dense plant canopies and prolonged leaf wetness periods recorded the highest disease levels. No host resistance was observed among the farmer-preferred local varieties sampled, highlighting the vulnerability of current production systems. The study recommends evaluation of improved soybean varieties with documented resistance to Cercospora leaf spot under local agroecological conditions. Extension services should also be strengthened to improve disease identification capacity among North East Nigerian soybean farmers. Keywords: soybean, Cercospora sojina, Borno State, leaf spot, disease incidence.