Antifungal and Seedling Growth-Promoting Effects of Neem (Azadirachta indica A. Juss.), Onion (Allium cepa L.) and Ginger (Zingiber officinale R.) Extracts as Seed Treatments for Maize (Zea mays L.)

Abstract

Seed-borne fungi are important constraints to maize seed quality because they can reduce germination and seedling vigor, while synthetic seed dressings may be costly and environmentally undesirable for smallholder farmers. This study evaluated aqueous and alcoholic extracts of neem (Azadirachta indica) leaves, onion (Allium cepa) bulbs, and ginger (Zingiber officinale) rhizomes at 10, 20, and 30% (w/v) concentrations for their in vitro antifungal activity against fungi isolated from maize and their effects on maize germination and early seedling growth. Four fungi were identified morphologically: Aspergillus niger, A. flavus, Penicillium spp., and Fusarium oxysporum. Alcoholic extraction produced significantly higher yields than aqueous extraction, with yields of 17.2% versus 12.2% for neem, 14.7% versus 12.1% for ginger, and 13.4% versus 10.1% for onion (p = 0.021). In the poisoned food assay, mycelial growth inhibition increased with extract concentration across the tested extracts and fungi. The highest inhibition (53.9%) was recorded with 30% aqueous neem extract against F. oxysporum. Solvent type did not significantly affect inhibition for any extract–pathogen combination (p > 0.05). Seed treatment with the extracts did not impair germination. Germination ranged from 40.0 to 100% and increased significantly with extract concentration for each plant extract (p < 0.0001), with the highest germination (100%) recorded for 30% aqueous ginger extract. Alcoholic neem extract produced significantly longer roots (p = 0.0142) and shoots (p = 0.0235) than aqueous neem extract. Overall, the extracts demonstrated moderate, concentration-dependent antifungal activity without evident phytotoxic effects on maize at the concentrations tested.