The problem of how to feed an ever increasing human population, in a sustainable fashion, is probably one of the most intractable issues facing humankind today. The widespread use of expensive agrichemicals for the control of disease not only reduces biodiversity in the soil but may also eventually lead to the development of pathogen resistance if overused. In Europe, the array of agrichemicals on the market is being reduced, in part due to heightened consumer sensitivities with respect to product safety. For agriculture to become sustainable, plant disease-control strategies must become more ecologically friendly with lower inputs. A biological approach which includes the use of beneficial microbes offers an alternative and more sustainable solution. It has been proposed as an alternative to chemical-based approaches for the suppression of plant pathogens and the control of plant diseases in an integrated pest management system. In recent years, the plant pathogen-suppressing action of rhizobacterial volatiles has attracted attention with regard to biological control applications. The beneficial microbes, in the absence of physical contact with plants, release a wide range of volatile organic compounds (VOCs), which may be one mechanism for how these bacteria influence plant health and induce systemic resistance (ISR). Our research project VALORAM ‘Valorizing Andean microbial diversity through sustainable intensification of potato-based farming systems‘ aims at exploring the existing large biodiversity of soil micro-organisms of Andean countries for the development of alternative, efficient technologies and crop management practices to improve the sustainability, food security, environmental protection and productivity of Andean cropping systems, benefiting rural farming households. During the course of our research in VALORAM, laboratory and field-based studies were carried out in order to examine the plant growth promotion and disease suppression potential of rhizobacteria that had been isolated from the rhizosphere of potato in the central Andean highlands. Of ~670 rhizobacterial isolates, ~30 isolates showed antagonistic activity against R.solani and P.infestans on plate assays. Many of the isolates were positive in a number of functional assays including indole acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, phosphate solubilisation, ammonia and HCN production. During growth-room experiments, 23 isolates were associated with growth promotion and/or disease suppression. Gas chromatography coupled with mass spectrometry (GC/MS) was used to detect VOCs produced by rhizobacteria. Volatile analysis of the rhizobacterial strains revealed a range of volatile organic compounds including 2,3-butanediol which is known to be involved in plant growth promotion and in induced systemic resistance. A number of antifungal compounds were detected including 2-hexen-1-ol. In split plate assays, we found that pure synthetic 2-hexen-1-ol can also inhibit R.solani. Field trials were carried out with a selection of these rhizobacterial strains in their respective countries of origin i.e Bolivia, Ecuador and Peru. Of the isolates deployed in the field, some showed a significant response in terms of disease suppression and plant-growth promotion. We suggest that this approach, using appropriate deployment strategies, may offer promise as part of a low-input integrated pest management system.
The research project “VALORAM - Valorizing Andean microbial diversity through sustainable intensification of potato-based farming systems” was supported by European Commission’s Seventh Framework Program FP7/2007-2013 under grant agreement No 227522, 01/02/2009-31/01/2014.