Isolation, Identification and Pathogenicity of Collar Rot of Groundnut (Arachis hypogaea) Caused by Aspergillus niger van Tieghem

Groundnut (Arachis hypogaea L.) is an economically important legume crop in India and many other countries worldwide. Groundnut cultivation is affected by many biotic and abiotic stresses. Among biotic stresses, groundnut is attacked by many fungal, bacterial and viral pathogens. The most harmful fungal diseases are Collar rot, stem rot, rust and other soil borne diseases. Collar rot caused by Aspergillus niger is one of the most important disease of groundnut extensive in India and worldwide. In this study, symptomatic infected plant samples were collected from different locations in Rajasthan, Isolated fungal species were identified on the basis of morphological characterization. The groundnut plant had common symptoms, including the first appearance of seedling rotting in the cotyledon and hypocotyl areas following germination, followed by drying and wilting of lateral branches and whole plant died. Microscopic examinations of the temporary mounts prepared from Aspergillus niger affected groundnut plant specimens and pure culture of A. niger revealed mycelia were septate, hyaline and conidiophores were long with spherical vesicles at the apex, conidia were globose, brown to black in color. The pathogenicity of A. niger was evaluated under pot house circumstances on the GJG-19 variety of groundnut using seed and soil inoculation methods, thereby confirming Koch's Postulate. The artificial inoculated plants exhibited pre-emergent rot of seed and post-emergent rot with appearance of a circular, brownish spot on the cotyledons. The discolored area rapidly became soft and rotten and spread on to the stems and hypocotyls which become yellow, soft, rotten and collapse. Greyish white mycelium and black fructifications of the pathogen appeared on the surface of the affected parts.