Etiology and management of leaf spot disease of arecanut in northern Kerala By: Bhavana, A S

Abstract

The study entitled “Etiology and management of leaf spot disease of arecanut in Northern Kerala” was carried out in the Department of Plant Pathology, College of Agriculture, Padannakkad during 2023-2025 with the objective of etiology of the fungal pathogen/s associated with the leafspot disease of arecanut and to formulate management strategies against the disease. A purposive sampling survey was conducted in four AEUs of Kasaragod and Kannur districts to collect infected and healthy leaf of arecanut leaf spot disease affected palms samples. The fungi associated with the leaf spot symptoms were isolated and characterised. Pathogenicity tests revealed that twelve isolates were pathogenic, producing symptoms within 12–15 days after inoculation. These twelve pathogenic isolates were subsequently sent to the Rajiv Gandhi Centre for Biotechnology (RGCB), Thiruvananthapuram, for molecular characterization. Among the six isolates three isolates showed high similarity with Colletotrichum arecicola which is reported for the first time on arecanut in India. The contents of nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), and boron (B) were analysed in both healthy and diseased leaf samples collected from various locations and AEUs. A total set of healthy and diseased leaf samples were analysed using standard protocols. It was found that K level was consistently higher in healthy samples compared to diseased ones, indicating the role of K in enhancing disease resistance. Nitrogen and magnesium showed variable patterns depending on the AEU and did not follow a uniform trend. Calcium content was generally higher in healthy leaves, except in the leaves collected from AEU 13. Boron levels tended to be higher in diseased leaves suggesting a possible stress induced accumulation. Phylloplane microorganisms were isolated from the healthy arecanut leaves. These were evaluated for antagonism towards Colletotrichum arecicola using dual culture technique. Among them, two Trichoderma- like fungal isolates and one-gram negative bacterial isolate exhibited strong inhibition of the predominant pathogen C. arecicola. Under in vitro evaluation of fungicides against C. arecicola by poison food technique, mancozeb (75WP) at 0.2%, propiconazole (25EC) at 0.2% and carbendazim 12% + mancozeb 63% (75 WP) at 0.2% exhibited high inhibition (100%). These three fungicides, along with the antagonists selected from phylloplane used for in vivo evaluation against the disease. Fungicides and antagonists were applied one week after pathogen inoculation on leaves. After 15 days of fungicide application, propiconazole (25 EC) at 0.2% and carbendazim 12% + mancozeb 63% (75 WP) at 0.2% were found effective against arecanut leaf spot. The study identified as C. arecicola is the major cause of arecanut leaf spot in Northern Kerala, and it reported for the first time on arecanut in India. Nutrient analysis showed that higher potassium levels were associated with healthier leaves. Among the management options tested, propiconazole (25 EC) at 0.2% and carbendazim 12% + mancozeb 63% (75 WP) at 0.2% were the most effective in reducing disease severity. The findings are helped to learn more about the etiology of the leaf spot disease and in developing improved fungicide and fertilizer schedules for managing arecanut leaf spot disease.