Arbuscular mycorrhizal fungi alter antifungal potential of lemongrass essential oil against Fusarium solani, causing root rot in common bean (Phaseolus vulgaris L.)

The variation in chemical composition of essential oils (EOs) as affected by plant phenology and environmental factors is a crucial limitation in standardization of EOs and thus their effective implementation into novel organic farming. The cultivation of medicinal and aromatic plants (MAP) using bio-elicitors has been advocated as genuine tool to sustainably assure higher quantity and quality EOs. Herein, a field trial and laboratory bioassays were undergone to decipher the impact of a local arbuscular mycorrhizal fungi (AMF) inoculation on agromorphological yield, EO output and differential suppression of common bean (Phaseolus vulgaris L.) root rot incited by Fusarium solani. The field experiment was laid out following a completely randomized block design (CRBD) with two treatments; non-inoculated control and AMF-inoculation in triplicates. The effects of the EOs were tested against mycelial growth, conidia and common bean seeds germination. Promising concentrations were thereafter assessed for their suppressive effect against Fusariun solani in planta. A significantly higher collar diameter, hypocotyl branching and subsequent Mycorrhizal Dependency (MD) in mycorrhizal lemongrass [(thorn) AMF] compared to non-inoculated counterpart [(-)AMF]. The resulting EOs consistently repressed F. solani Fs4 conidia germination and mycelium deployment in a dose-dependent manner, with minimum inhibitory concentration (MIC) of 500 ppm for both the EOs, and 125 ppm for the reference fungicide (Ridomil Plus 44 WP). The EO from mycorrhizal lemongrass protected the common bean plantlets from infection by F. solani Fs4 both in laboratory and greenhouse conditions, leading to healthier and vigorous plantlets. The best protection rate was once more obtained with EO from AMF-primed lemongrass at the concentration of 1000 ppm (65.0%) while the lowest disease severity was obtained with Ridomil Plus 44 WP (63.13%). Overall, AMF inoculation shifted the lemongrass biochemical processes with subsequent impact on growth, and an enhanced suppression in Fusarium root rot under greenhouse conditions.