This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Plants might seem helpless when it comes to insect attacks, but they are known to employ various techniques to deter pests. One of these techniques involves sending out signals to recruit parasitoid wasps, and a new study, published in Cell Reports, has found that at least one plant can extend this deterrent system to future generations growing in the same soil.
Some plants use tiny hairs to slow down insects or thorns to deter larger animals from grazing. Others use toxic chemicals to make themselves taste bad. Still others release airborne scents, called herbivore-induced plant volatiles (HIPVs), that attract predators like parasitoid wasps.
However, studies have shown that these HIPVs usually fade quickly when the insects are no longer a threat, meaning the method results in a seemingly temporary fix. Researchers have also found that root chemistry and soil microbes are sometimes altered when insects feast on leaves, but the consequences for attracting natural enemies were unclear. The authors of the new study write, "Plants continuously interact with the soil environment through root exudates, the complex mixtures of primary and specialized metabolites that shape the composition and activity of rhizosphere microbial communities.
These microbial communities, in turn, exert profound effects on plant growth, nutrient acquisition, and resistance to pathogens and herbivores, forming dynamic plant-soil feedbacks. Recent studies have begun to reveal that leaf herbivory can modify root exudation profiles and restructure rhizosphere microbiota." To determine whether certain plant defenses can persist over time with the assistance of soil microbes rather than only through short-lived airborne signals, the team conducted a series of experiments with cowpea plants. Cowpea plants are often afflicted by leafminer feeding but are known to employ airborne signals that attract parasitoid wasps, which feed on the leafminers, thereby saving the plant.
The team grew new cowpeas in soil previously occupied by either attacked or unattacked plants and combined insect-choice tests with plant chemical, gene-activity, volatile and soil-microbiome measurements. They sterilized the soil and then reintroduced the microbial population, used chemical treatments and tested individual bacterial inoculations to determine cause and effect. Results showed that cowpea plants attacked by leafminers changed their surrounding soil in ways that benefited the next generation of plants.
The new, uninfested cowpeas grown in the conditioned soil attracted more parasitoid wasps and also grew bigger. The researchers determined that leaf damage from the insects activated a plant defense hormone called jasmonate, which prompted roots to release more of two flavonoid compounds, daidzein and genistein. The compounds then selectively reshaped the soil microbiome, enriching several Bradyrhizobium bacteria.
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