Bioformulations of Entrophospora lutea enriched with biostimulants for growth promotion and control of Rhizoctonia root rot in lupine

Abstract

Arbuscular mycorrhizal fungus (AMF) Entrophospora lutea was previously selected as a highly compatible isolate for lupine, and the main objective of the present study was to further improve its performance and practical applicability by developing two E. lutea formulations using peat and vermiculite carriers enriched with various biostimulants. Incorporating biostimulants into AMF formulations can enhance fungal performance and root symbiosis. The first formulation contained proline, ascorbic acid, and hemicellulose, whereas the second contained proline, humic acid, and mannitol. Both formulations improved AMF performance by increasing the number of infective propagules and root colonization rate. Their efficacy against Rhizoctonia root rot in lupine was evaluated in comparison with unamended E. lutea and the fungicide Rizolex under greenhouse and field conditions. Under greenhouse conditions, Formulation 2 increased plant survival to 92% and reduced disease severity to 24.2%, compared with 48% survival and 65.8% disease severity in the infected control. Root colonization reached 78% and 69% for Formulations 1 and 2, respectively, compared with 53% for the unamended E. lutea. These improvements were associated with enhanced plant growth, nodulation, nitrogenous activity, and enhanced antioxidant enzyme activities. Formulation 2 showed a more pronounced effect with increased proline accumulation and caused 82.6% reduction in H2O2 accumulation compared with the infected control. Under field conditions, both formulations improved yield compared with the untreated control across the two growing seasons. No significant differences were observed between the AMF formulations and Rizolex for most evaluated parameters. These findings demonstrate that the developed biostimulants-enriched AMF formulations are effective and environmentally friendly alternatives to chemical fungicides for controlling R. solani root rot in lupine, while improving plant growth and productivity.