Histopathological Studies of African Yam Bean Seeds and Seedling Infection by Aspergillus niger

Background and Objective: Aspergillus niger is a common fungal pathogen that infects African yam bean seeds and seedlings, leading to significant agricultural losses. Histopathological studies of African yam bean seeds and seedling infection by Aspergillus niger were conducted using light microscopy. The detection and isolation of seed-borne fungi were done using potato dextrose Agar. Materials and Methods: Eighty samples, each of the Light brown TSs 152 accessions, Reddish brown TSs 138, and smooth brown variety of the African yam bean seed were collected from Orie Ugba Market in Umuahia around July, 2021. The Standard Blotter Method was used to inoculate fungal organisms, which were then isolated and investigated for their pathogenicity using a foliar drop method in a greenhouse. Koch’s postulates were confirmed through reinfection of AYB seedlings with spore suspension, dose dependent effects, and disease development for 10 days. Anatomical transverse sectioning was performed on African yam bean seeds and seedlings to determine fungus position and distribution, using rotating microtomes and histological procedures. Means were compared using the Least Significant Difference (LSD) test at a 0.05 significance level. Results: Aspergillus niger, a pathogen, was found in African yam bean seeds, causing necrotic leaf spots, blight, and defoliation. Pathogenicity tests confirmed the infection, and anatomical sections showed a dense mycelium mass in the seed coat, embryo, endosperm, and aleurone layer. The mycelium invaded epidermal cells, progressed through parenchyma tissues, and caused complete degradation within phloem and xylem vessels. The study found mycelium colonization on the epidermis and xylem vessels, leading to vascular tissue disintegration and blockage. Conclusion: The study reveals that Aspergillus niger significantly damages African yam bean seeds by colonizing and degrading vascular tissues. Its pathogenic effects include necrotic leaf spots, blight, and defoliation.