Antimicrobial Terpenes Suppressed the Infection Process of Phytophthora in Fennel-Pepper Intercropping System

Abstract

The interactions between non-host roots and pathogens may be key to the inhibition of soilborne pathogens in intercropping systems. Fennel (Foeniculum vulgare) can be intercropped with a wide range of other plants to inhibit soilborne pathogens in biodiversity cultivation. However, the key compounds of fennel root exudates involved in the interactions between fennel roots and pathogens are still unknown. Here, a greenhouse experiment confirmed that intercropping with fennel suppressed pepper (Capsicum annuum) blight disease caused by Phytophthora capsici. Experimentally, the roots and root exudates of fennel can effectively interfere with the infection process of P. capsici at rhizosphere soil concentrations by attracting zoospores and inhibiting the motility of the zoospores and germination of the cystospores. Five terpene compounds (D-limonene, estragole, anethole, gamma-terpenes, and beta-myrcene) that were identified in the fennel rhizosphere soil and root exudates were found to interfere with P. capsica infection. D-limonene was associated with positive chemotaxis with zoospores, and a mixture of the five terpene compounds showed a strong synergistic effect on the infection process of P. capsici, especially for zoospore rupture. Furthermore, the five terpene compounds can induce the accumulation of reactive oxygen species (ROS), especially anethole, in hyphae. ROS accumulation may be one of the antimicrobial mechanisms of terpene compounds. Above all, we proposed that terpene compounds secreted from fennel root play a key role in Phytophthora disease suppression in this intercropping system.

Nematicidal plants for root-knot nematode (Meloidogyne spp.) management in vegetable cropping systems

“…Like Tagetes, perhaps F. vulgare's mechanism of action is mainly at the rhizosphere level by being a hatching inhibitor, repellent/ toxic to the juveniles, or killing the J2 upon attempt to penetrate the root, with further activity to sti e the establishment of those that would have successfully penetrated inside. Five terpene compounds-D-limonene, estragole, anethole, gammaterpenes, and beta-myrcene-were identi ed in fennel rhizosphere soil and root exudates (Yang et al 2022). These compounds were found to inhibit Phytophthora capsica infection.…”

“…D-limonene, in particular, attracted zoospores through positive chemotaxis. The combined effect of all ve terpenes showed a strong synergistic action, signi cantly disrupting the infection process by causing zoospore rupture (Yang et al 2022).…”

Repeated exposure of wheat to the fungal root pathogen Bipolaris sorokiniana modulates rhizosphere microbiome assembly and disease suppressiveness

“…Bacterial terpenes are implicated in interkingdom signaling, as these volatile compounds elicit responses from plants [ 45 ]. Terpenes were also found to be associated with the suppression of Phytophthora capsici in the Foeniculum vulgare rhizosphere [ 46 ]. Terpenes BGCs identified in our study were affiliated to a number of bacterial taxa responsive to pathogen exposure, as pointed by amplicon sequencing data.…”

Soil and Phytomicrobiome for Plant Disease Suppression and Management under Climate Change: A Review

“…For instance, intercropping maize with Atractylodes lancea (a traditional Chinese medicinal plant) acidified the rhizospheric soil and promoted the accumulation of beneficial PGPR such as Streptomyces , Bradyrhizobium , Candidatus Solibacter, Gemmatirosa , and Pseudolabrys , benefiting the growth of A. lancea [ 77 ]. In a fennel–pepper intercropping system, five terpene substances discovered in the soil and root exudates of the fennel rhizosphere (d-limonene, estragole, anethole, gamma-terpenes, and beta-myrcene) were found to inhibit Phytophthora capsici [ 78 ]. Similar observations were made in maize–soybean intercropping, where maize root exudates, such as cinnamic acid, vanillic acid, ferulic acid, and p -coumaric acid, inhibited Phytophthora sojae , the causative agent of Phytophthora blight in soybean [ 79 ].…”