Abstract
Plant protection with beneficial microbes is considered to be a promising alternative to chemical control of pests and pathogens. Beneficial microbes can boost plant defences via induced systemic resistance (ISR), enhancing plant resistance against future biotic stresses. Although the use of ISR-inducing microbes in agriculture seems promising, the activation of ISR is context-dependent: it often occurs only under particular biotic and abiotic conditions, thus making its use unpredictable and hindering its application. Although major breakthroughs in research on mechanistic aspects of ISR have been reported, ISR research is mainly conducted under highly controlled conditions, differing from those in agricultural systems. This forms one of the bottlenecks for the development of applications based on ISR-inducing microbes in commercial agriculture. We propose an approach that explicitly incorporates context-dependent factors in ISR research to improve the predictability of ISR induction under environmentally variable conditions. Here, we highlight how abiotic and biotic factors influence plant–microbe interactions in the context of ISR. We also discuss the need to raise awareness in harnessing interdisciplinary efforts between researchers and stakeholders partaking in the development of applications involving ISR-inducing microbes for sustainable agriculture.
Highlights
In the last decades, the interest in using beneficial microbes in agriculture has grown significantly due to their ability to improve plant resistance against pathogens and insect pests and to increase tolerance to abiotic stressors [1,2]
We will focus on beneficial effects of microbes on crop protection that are mediated through induced systemic resistance (ISR) and the challenges associated with their application in sustainable agriculture and horticulture
The molecular mechanisms involved in the onset of ISR are often studied at the root level where the plant recognises the beneficial microbe through microbeassociated molecular patterns (MAMPs) and a local signal is generated that cascades to the rest of the plant tissues
Summary
The interest in using beneficial microbes in agriculture has grown significantly due to their ability to improve plant resistance against pathogens and insect pests and to increase tolerance to abiotic stressors [1,2]. ISR as one of their effects (Table 1) are not sold as ISR products per se, but, for example, as biostimulants or as biofertilizers even though a reduction of pathogen or pest damage through their activation of ISR may contribute to their enhancement of crop production When they are registered as biopesticides, this is predominantly based on their direct fungicidal, nematicidal or pesticidal effects mediated by direct antibiotic or cell lytical effects and not necessarily on their indirect, plant-mediated effects, i.e., their potential to induce ISR (Table 1). The authors apologize to all the researchers whose work could not be included because of space limitations. 2 For some entomopathogenic fungi, plant-mediated protective effects of these microbes have been shown, it has not been corroborated whether they are ISR-related events
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