Evaluation and Management of Alternaria Blight of Onion

Abstract

Onion (Allium cepa L.) is an economically important bulb and seed crop, and Alternaria blight caused by Alternaria porri is one of the major constraints to onion seed production. The present investigation was undertaken to evaluate the efficacy of selected fungicides and bioagents for the management of Alternaria blight under laboratory and field conditions. The associated pathogen was isolated from diseased onion leaves and identified as A. porri based on its cultural and morphological characteristics. Under in vitro conditions, Propiconazole (T₆) exhibited the highest mycelial growth inhibition, followed by Carbendazim + Mancozeb (T₈) and Azoxystrobin + Difenoconazole (T₇). Among the bioagents, Trichoderma harzianum showed the maximum inhibition (74.33%), followed by T. asperellum and Pseudomonas fluorescens. The promising treatments were subsequently evaluated under field conditions through bulb treatment followed by foliar application of fungicides and bioagents. Propiconazole (T6) was the most effective treatment in suppressing Alternaria blight, recording the highest per cent disease control, followed by Azoxystrobin + Difenoconazole (T7) and Carbendazim + Mancozeb (T8). In contrast, the untreated control (T12) recorded the highest disease intensity at harvest. Disease suppression was associated with a marked improvement in onion seed production. Propiconazole (T6) recorded the highest seed yield (1045 kg ha-1), followed by Azoxystrobin + Difenoconazole (T7) (970 kg ha-1) and Carbendazim + Mancozeb (T8) (945 kg ha-1), compared with 605 kg ha-1 in the untreated control. The findings demonstrated that integrated use of bulb treatment and subsequent application of fungicides and bioagents, particularly Propiconazole, can effectively reduce Alternaria blight and enhance onion seed yield under field conditions.