Endophytic bacteria, from the desert spurge (Euphorbia antiquorum) enhance nutrients uptake and suppress root rot in the common bean

Abstract

Global agriculture has long been concerned with the management of soil-borne diseases. Owing to their occurrence under the ground surface, coupled to the soil long-lasting anatomic structures such as conidia and chlamydospores formed by their causative agents, the latter are especially tricky to diagnose, identify and effectively manage. In this study, we evaluated the fungitoxic effects and nutrient mobilising abilities of 36 endophytic bacteria derived from the "desert spurge" (Euphorbia antiquorum L.) against Fusarium solani, Fusarium oxysporum, and Macrophomina phaseolina, the principal causative agents of common bean root rot in Cameroon. The antagonistic potentials of the biocontrol agents (BCAs) were assessed using conventional direct and indirect antagonism tests. The shortlisted candidates were thereafter evaluated for their in planta suppressive effects in a climate-controlled greenhouse in a completely randomised block design layout. Bacillus amyloliquefaciens BFL2, Bacillus velezensis BE1, and Pseudomnas aeruginosa RR4 produced wide spectrum hydro-soluble antifungal metabolites, with inhibitory percentages culminating at 80.79% vis-a-vis Fusarium solani Fs4. Likewise, with reference to Fusarium oxysporum NG22, the BCAs; Unidentified LPR3+ (84.25%) and Lyncinibacillus fusiformis RR7 (90.75%) released the most harmful volatile organic metabolites (VOM). Root rot incidence (75.4%) and severity (60.54%) were dramatically reduced after seed bacterization with B. amyloliquefaciens RA37, a far better outcome compared to Carbendazin (47.29%), a synthetic fungicide. Ultimately, N, P, K, Cu, Zn, Fe, and Mn contents, as well as overall plant vigour, were fostered by some BCAs. These findings demonstrate the remarkable biocontrol abilities of B. amyloliquefaciens RA37, opening a path to a biological solution to bean root rot.