Manipulation of Chemically Mediated Interactions in Agricultural Soils to Enhance the Control of Crop Pests and to Improve Crop Yield

Abstract

In most agro-ecosystems the organisms that feed on plant roots have an important impact on crop yield and can impose tremendous costs to farmers. Similar to aboveground pests, they rely on a broad range of chemical cues to locate their host plant. In their turn, plants have co-evolved a large arsenal of direct and indirect defense to face these attacks. For instance, insect herbivory induces the synthesis and release of specific volatile compounds in plants. These volatiles have been shown to be highly attractive to natural enemies of the herbivores, such as parasitoids, predators, or entomopathogenic nematodes. So far few of the key compounds mediating these so-called tritrophic interactions have been identified and only few genes and biochemical pathways responsible for the production of the emitted volatiles have been elucidated and described. Roots also exude chemicals that directly impact belowground herbivores by altering their behavior or development. Many of these compounds remain unknown, but the identification of, for instance, a key compound that triggers nematode egg hatching to some plant parasitic nematodes has great potential for application in crop protection. These advances in understanding the chemical emissions and their role in ecological signaling open novel ways to manipulate plant exudates in order to enhance their natural defense properties. The potential of this approach is discussed, and we identify several gaps in our knowledge and steps that need to be taken to arrive at ecologically sound strategies for belowground pest management.

Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

“…When released by insect-damaged maize roots, (E)-β-caryophyllene was identified as the main belowground chemical attractant for entomopathogenic nematodes (Heterorhabditis megidis Poinar, Jackson & Klein and Heterorhabditis bacteriophora Poinar) in laboratory and field experiments (Rasmann et al 2005;Turlings 2007, 2008;Hiltpold et al 2010a). The discovery that a root-emitted signal produced by plants infested by D. virgifera virgifera larvae is able to recruit organisms of the third trophic level as an indirect plant defence mechanism led to the development of new crop protection strategies using entomopathogenic nematodes as biological control agents to reduce D. virgifera virgifera emergence and root damage in the field (Hiltpold et al 2010c;Hiltpold and Turlings 2012). Several attempts to improve the searching efficiency of entomopathogenic nematodes were made, notably by selecting an entomopathogenic nematode strain for enhanced responsiveness to (E)-β-caryophyllene (Hiltpold et al 2010a, b) or by genetically engineering a maize variety that had lost the ability to produce (E)-β-caryophyllene in order to restore the release of the sesquiterpene signal (Degenhardt et al 2009).…”

Rethinking how volatiles are released from plant cells

“…These metabolites, when released from leaves, flowers, and fruits into the atmosphere, and from roots into the soil, have key roles in the attraction of pollinators [2] and seed dispersers [3,4], above-and belowground defense against herbivores [5][6][7][8], protection against pathogens [9,10], and plant-plant signaling [11,12]. Certain VOCs are also able to protect plants against abiotic stresses, such as high light, temperature, or oxidative stress [13][14][15].…”

Behavioral Response of Grape Root Borer (Lepidoptera: Sesiidae) Neonates to Grape Root Volatiles

“…Studies using various bioassay approaches have shown that chemical cues from intact roots (Johnson et al 2004), solvent-based root extracts (Kamm and Buttery 1984, Tapia et al 2005, Bergh et al 2011, or root volatiles (Matsumoto and Thorsteinson 1968, Jones and Coaker 1979, Soni and Finch 1979, Koštál 1992, Wenke et al 2010, Manosalva et al 2011) from host plants elicited positive behavioral responses by root-feeding insects. Chemically mediated interactions between root-feeding insects and their speciÞc host plants were reviewed most recently by , Hiltpold and Turlings (2012), and Johnson and Nielsen (2012). Bergh et al (2011) showed that recently eclosed grape root borer neonates were recorded more frequently on or near Þlter paper discs treated with ethanol-based grape root extracts than untreated discs or those treated with a nonhost (apple) root extract in single extract bioassays.…”