Endophytic Aspergillus fumigatus modulates growth, oxidative stress, and cadmium accumulation in okra under salinity and heavy-metal stress

Abstract

Abiotic stress factors, such as salinity and heavy metals (HM), significantly reduce okra (Abelmoschus esculentus L.) yield, an important vegetable crop cultivated globally. The symbiotic relationship between endophytic fungi and plants enhances plant growth and helps plants overcome such stresses. This study was designed to isolate and examine endophytic fungi from Ziziphus lotus roots for their growth-promoting potential under salt (250 mM NaCl) and cadmium (100 ppm Cd) stress. The growth of okra was significantly enhanced by inoculation with Aspergillus fumigatus (SOA), resulting in a 28.9% increase in plant height (33.24 cm vs. 25.79 cm in the control) and improved biomass, chlorophyll content, and phytohormone regulation. Chlorophyll A content rose by 108.4% in SOA-treated plants (4.894 mg/g FW) relative to control (2.348 mg/g FW), while shoot dry weight increased more than threefold (4.365 g vs. 1.42 g in control). Abscisic acid (ABA) content decreased in SOA-treated plants, indicating a reduced stress response, whereas enhanced gibberellic acid (GA) and indole-3-acetic acid (IAA) content promoted growth. Biochemical analysis revealed higher accumulation of lipids, sugars, phenols, and flavonoids, resulting in improved stress adaptation. Oxidative damage was reduced through high antioxidant enzyme activities (CAT and POD). SOA modulated cadmium uptake, thereby reducing heavy metal toxicity. These findings showed that endophytic fungi have the potential to enhance plants’ resilience and provide a promising controlled-environment approach to enhance crop productivity in metal- and salt-contaminated soils.