Potency of formulated biocontrol agents from lab to field: a sustainable approach for onion purple blotch suppression

Purple blotch disease incited by Alternaria porri is the major constraint in onion seed production, adversely affecting the quantity and quality of the seed. The indiscriminate and injudicious application of chemical pesticides has led to significant repercussions on both the environment and the overall well-being of living organisms, hence there is an urgent call for a transformative shift towards eco-friendly and sustainable approaches for combating the challenges posed by plant pathogens. In this context, the present study highlights the potency of formulated bio agents in enhancing seed vigour and suppressing onion purple blotch disease. Amongst the four bio agent formulations (Trichoderma harzianum 2.0% WP, Trichoderma viride 1.0% WP, Bacillus subtilis 1.50% LF and Pseudomonas fluorescens 1.75% WP) evaluated for priming impact on onion seedlings, Trichoderma harzianum 2.0% WP exhibited predominance in enhancing seed quality parameters with maximum seedling emergence (73.00 per cent), length (11.24 cm), dry weight (16.02 mg) and vigour indices I (818.63) and II (1168.61). This, in turn, led to maximum enhancement in total soluble sugars, total soluble phenolics, total chlorophyll content, polyphenol oxidase and peroxidase. All the investigated biochemical parameters revealed a positive correlation with vigour indices of seedlings. Trichoderma harzianum 2.0% WP (81.17 per cent) resulted in the maximum reduction in mycelial development of Alternaria porri. The potency of bio formulations under field conditions also exhibited supremacy of Trichoderma harzianum 2.0% WP with maximum disease management (23.08 per cent) representing AUDPC value (623.00), consequently leading to maximum increase in seed yield over control (5.61 per cent). Trichoderma harzianum 2.0% WP could be employed for long-term management of onion purple blotch.