Effect of tomato-mediated soil microbials on the olfactory orientation of greenhouse pest natural enemies

Abstract: Tomato crops are constantly threatened by a number of pests. Root-associated
microorganisms, such as plant growth promoting fungi (PGPF) and rhizobacteria (PGPR), are
known to enhance plant defences. However, the role of volatiles emitted by icrobialinoculated tomatoes on the olfactory response of biocontrol agents of tomato pests needs further
investigation. The olfactory response of three natural enemies (Cryptolaemus montrouzieri,
Eretmocerus eremicus and Nesidiocoris tenuis) used against greenhouse key pests to volatiles emitted by tomato plants previously inoculated with PGPF and PGPR were assessed in a twoway olfactometer in the laboratory. Three commercial fungal strains (Trichoderma asperellum, T. harzianum and Beauveria bassiana ATCC 7404), and six bacterial species (commercial strains of Bacillus subtilis and B. amyloliquefaciens, and laboratory isolates of B. spizizenii, Pseudomonas fluorescens, P. veronii and P. gessardii) were tested after 3 and 7 days of inoculation (doi) in comparison to untreated plants. Tomato emitted volatiles and the expression level of defense-related genes in plant tissues were also assessed through GC-MS and qRTPCR, respectively. In dual choice tests, C. montrouzieri showed significant attraction towards tomato plants inoculated with B. spizizenii and T. asperellum after 3 and 7 doi, respectively. Conversely, C. montrouzieri females were generally repelled by tomato emitted volatiles when inoculated with other microbials. A similar trend was observed with E. eremicus. Tomato plants inoculated with B. bassiana and B. subtilis significantly repelled N. tenuis both after 3 and 7 doi. The tomato-emitted volatile profile and the transcriptome of plant defence-associated pathways supported our results. These findings suggest that future research into multitrophic interactions can be considered when combining microbials with arthropod natural enemies for Integrated Pest Management in greenhouse tomato systems.