Interactions of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi and their potential in bioformulations for potato cropping

Ecuadorian farmers often cultivate potatoes under high-input systems with the subsequent risks for the environment and farmer’s health. An alternative to reduce the use of agrochemicals is by applying beneficial soil microorganisms such as arbuscular mycorrhizal fungi (AMF) and Plant Growth Promoting Rhizobacteria (PGPR). However, the PGPR and AMF interactions have been little explored in order to formulate efficient consortia-based inoculants. A preliminary field experiment showed that inoculation of potato with commercial AMF products did not improve tuber yield likely due to scarce establishment of the AMF. Hence, in the present study we aimed to: (1) evaluate the interactions between AMF and several PGPR when co-entrapped in alginate beads in order to increase the root colonization of the AMF in potato plants; (2) assess the effect of co-inoculation of AMF and PGPR on the elicitation of induced systemic resistance of potato plants and (3) evaluate the effect of crude extracts produced by two PGPR on the root colonization of potato by one AMF. Our results showed that a suitable AMF-PGPR combination could improve the AMF root colonization of potato. Further, PGPR-AMF co-inoculation of potato plants led to an activation of the plant systemic defense system via ethylene response factor 3 (ERF3) in presence of the fungal pathogen Rhizoctonia solani. Finally, the development of the AMF was stimulated by crude extracts produced by one PGPR isolate. Co-inoculation/co-entrapment of suitable AMF-PGPR combinations can promote the root colonization by the AMF and the activation of plant defense system; this effect can be enhanced by the addition of certain PGPR metabolites. Encapsulation technology may represent an innovative method to formulate efficient consortia-based inoculants for potato cropping.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201