Microbial Interactions in the Phyllosphere Increase Plant Performance under Herbivore Biotic Stress

Area of Science:

• Microbial ecology
• Plant-microbe interactions
• Plant pathology

Background:

• The phyllosphere harbors diverse microbes, but their roles in plant health under herbivory are unclear.
• Understanding bacterial colonization and survival is crucial for plant performance.
• Limited knowledge exists on how pathogenic and beneficial bacteria interact in the phyllosphere throughout a plant's life cycle.

Purpose of the Study:

• To investigate the colonization and survival of pathogenic and beneficial bacteria in the *Arabidopsis thaliana* phyllosphere.
• To determine the impact of these bacteria, alone and together, on plant performance under herbivory.
• To explore the influence of bacterial community composition and diversity on host plant fitness.

Main Methods:

• Experiments were conducted using four *Arabidopsis thaliana* accessions and three bacterial strains (*Pseudomonas syringae* DC3000, *Xanthomonas campestris*, and *Bacillus cereus*).
• Common garden conditions included fungus gnat herbivory (*Bradysia* spp.).
• Bacterial abundance, plant performance metrics (flowering time, biomass, siliques, seeds), and fitness were assessed.

Main Results:

• Plants showed greater *Bacillus cereus* abundance than pathogens in the phyllosphere.
• Arabidopsis accessions performed better with pathogens than with *B. cereus*, but all inoculated plants outperformed controls.
• Bacterial monocultures generally promoted plant growth more than mixed cultures, but species richness positively correlated with seed production.

Conclusions:

• Plant performance is enhanced when facing multiple natural enemies, suggesting induced defenses.
• Bacterial community composition significantly impacts phyllosphere dynamics and plant health.
• Bacterial species richness, rather than specific species dominance, may be more beneficial for host plant fitness under herbivory.