Root symbionts: Powerful drivers of plant above‐ and belowground indirect defenses

Abstract

Soil microbial mutualists of plants, including mycorrhizal fungi, nonmycorrhizal fungi and plant growth promoting rhizobacteria, have been typically characterized for increasing nutrient acquisition and plant growth. More recently, soil microbes have also been shown to increase direct plant defense against above-and belowground herbivores. Plants, however, do not only rely on direct defenses when attacked, but they can also recruit pest antagonists such as predators and parasitoids, both above and belowground, mainly via the release of volatile organic compounds (i.e., indirect defenses). In this review, we illustrate the main features and effects of soil microbial mutualists of plants on plant indirect defenses and discuss possible applications within the framework of sustainable crop protection against root-and shoot-feeding arthropod pests. We indicate the main knowledge gaps and the future challenges to be addressed in the study and application of these multifaceted interactions.

Pressures on soil functions from soil management in Germany. A foresight review

“…Developing plant varieties in terms of their pathogen tolerance and their defense mechanisms below ground is a research topic that may also become more practically relevant in the future once research has advanced (Johnson et al 2016;Rasmann et al 2017) (Table 5). New breeding technologies, such as CRISPR/cas9, can also lead to organisms, including varieties of annual agricultural crops, which can bring risks, such as harming ecosystems (Science for Environment Policy 2016) which could also have an impact on agricultural soils.…”

“…The Research bringing new insights into how to generate positive effects on plant production through microbial inoculation Johnson et al 2016;Saia et al 2015a;Saia et al 2015b;Zhang et al 2014;Verbruggen et al 2012;El-Sirafy et al 2006;Rasmann et al 2017;Kergunteuil et al 2016;Larkin 2015 Research, soil threats: generally positive effects on soil habitat function if pesticides can be avoided because of inoculation with natural enemies Kergunteuil et al 2016 Policies: If not studied and regulated enough, inoculants could reach the market that may affect non-targeted organisms negatively Kergunteuil et al 2016 Research bringing new insights on promoting local mutualists of crops and natural enemies of pests Johnson et al 2016;Rasmann et al 2017;Larkin 2015 Technology: improved methods to assess soil biota and derive management options expected ↑ Teagasc 2016…”

“…Important below ground mutualists for crops that can improve crop productivity and promote indirect plant defenses, among others when added by inoculation, are bacteria and fungi (Rasmann et al 2017). Positive effects on plant growth by soil inoculation with bacteria or fungi were found, for example, in wheat in Sicily (Saia et al 2015a), China (Zhang et al 2014), and Egypt (El-Sirafy et al 2006), whereas findings of negative effects (Verbruggen et al 2012) underline that the interdependencies are not well understood yet (Saia et al 2015b) (Table 7).…”

Mycorrhizae Alter Toxin Sequestration and Performance of Two Specialist Herbivores

“…In terrestrial ecosystems, both top-down and bottom-up forces travel with ease across the traditional soil "boundary, " with plants connecting the interactions that occur between above and belowground organisms (van der Putten et al, 2001;van Dam and Heil, 2011;Hunter, 2016). As a result, soil organisms that are associated with plant roots have the potential to affect herbivore populations above ground both by affecting plant quality for herbivores from the bottom-up (Hartley and Gange, 2009;Koricheva et al, 2009;Jung et al, 2012) and the resistance of herbivores to their natural enemies from the top down (Gange et al, 2003;Rasmann et al, 2017;Tao et al, 2017).…”

“…Rootassociated microbes, such as AMF, affect herbivore-natural enemy interactions indirectly by altering plant phenotype (Rasmann et al, 2017;Tao et al, 2017). For instance, AMF increase the attractiveness of plants to natural enemies by changing the volatile emissions of their host plants (Guerrieri et al, 2004;Fontana et al, 2009;Hoffmann et al, 2011;Schausberger et al, 2012;Babikova et al, 2013).…”