STUDIES ON Alternaria LEAF SPOT OF NIGER (Guizotia abyssinica L.)

Guizotia abyssinica L.commonly known as niger, is a traditional minor oilseed crop of India belonging to the family Compositae. The crop is attacked by several fungal, bacterial, viral, and phytoplasmal pathogens, among which leaf spot caused by Alternaria alternata has emerged as one of the most destructive diseases, leading to serious quantitative and qualitative yield losses. In the Konkan region of Maharashtra, the problem has intensified in recent years, demanding systematic investigation and effective management strategies. The disease typically appears first on older leaves as small, circular, dark brown spots with concentric rings and yellow halos. As infection advances, lesions enlarge and coalesce, resulting in blighting. The pathogen grows well on potato dextrose agar, producing olivaceous grey to black colonies with characteristic zonations. Morphologically, it bears septate mycelium and muriform, beaked conidia. Studies have shown that certain fungicides can completely suppress the pathogen in vitro, while bio-agents such as Pseudomonas fluorescens and species of Trichoderma significantly reduce its growth.