Efficacy of plant extracts in growth promotion and onion purple blotch management: Unveiling metabolite fingerprinting of promising neem leaf extracts through GC MS

Onion is affected by several biotic and abiotic stresses. This study aimed to evaluate the impact of onion seed priming with different plant extracts. The results show that neem leaf extract treated seeds exhibited the highest mean seedling establishment (71.50 per cent), seedling length (11.21 cm), seedling dry weight (15.88 mg) and seedling vigour indices (800.70 and 1135.27). The biochemical analysis of primed seedlings showed significant enhancement in enzymatic and non-enzymatic antioxidants. Purple blotch caused by Alternaria porri is the most important foliar disease of onion leading to significant losses. The evaluation of plant extracts against Alternaria porri showed that neem leaf extract at a concentration of 25 per cent inhibits mycelial growth of pathogen by 81.18 per cent. The GC MS analysis of the crude extract of neem indicated the presence of forty different chemical compounds, among which the main components included Benzene, 1,4-bis (phenylmethyl)- (15.05%), Naphthalene, 1,6-dimethyl- (10.98%), 3-(2,4-Dimethoxyphenyl) butan-2-one (8.63%) and Phytol (7.99%). Evaluation of the four promising botanicals viz., neem, congress grass, turmeric and ginger under field conditions indicated foliar sprays of neem leaf extract to be effective in both managing purple blotch disease (23.08 per cent disease management) and enhancing yield attributes (5.24 per cent seed yield increase). This study establishes the antimycotic and plant growth promoting potential of neem leaf extract for managing onion purple blotch.