Simultaneous Impact of Rhizobacteria Inoculation and Leaf-Chewing Insect Herbivory on Essential Oil Production and VOC Emissions in Ocimum basilicum.

Inoculation with rhizobacteria and feeding by herbivores, two types of abiotic stress, have been shown to increase the production of secondary metabolites in plants as part of the defense response. This study explored the simultaneous effects of inoculation with Bacillus amyloliquefaciens GB03 (a PGPR species) and herbivory by third-instar Spodoptera frugiperda larvae on essential oil (EO) yield and volatile organic compound (VOC) emissions in Ocimum basilicum plants. The density of glandular trichomes was also examined, given that they are linked to EO production and VOC emission. Herbivory increased EO content, but inoculation on its own did not. When combined, however, the two treatments led to a 10-fold rise in EO content with respect to non-inoculated plants. VOC emissions did not significantly differ between inoculated and non-inoculated plants, but they doubled in plants chewed by the larvae with respect to their undamaged counterparts. Interestingly, no changes were observed in VOC emissions when the treatments were tested together. In short, the two biotic stressors elicited differing plant defense responses, mainly when EO was concerned. PGPR did not stimulate EO production, while herbivory significantly enhanced it and increased VOC emissions. The combined treatment acted synergistically, and in this case, PGPR inoculation may have had a priming effect that amplified plant response to herbivory. Peltate trichome density was higher in inoculated plants, those damaged by larvae, and those subjected to the combination of both treatments. The findings highlight the intricate nature of plant defense mechanisms against various stressors and hint at a potential strategy to produce essential oil through the combined application of the two stressors tested here.

A practical method to investigate the effect of volatile organic compounds emitted by rhizobacteria on plant growth under conditions of salt stress.

Salinity is one of the causes that limit crop production. Plant Growth Promoting Rhizobacteria (PGPR) are beneficial soil bacteria that play a significant role in promoting plant growth. These microorganisms can produce their effect through the emission of Volatile Organic Compounds (VOCs). Most of the research to study the effects of microbial VOCs on plant growth has been carried out under controlled conditions using partitioned Petri dishes. In this article, we describe an alternative method that has the advantage of allowing long-term trials, being able to let the plant have a greater development in growth and height, without space limitation. In the proposed method, M. piperita were planted in glass jars containing Murashige and Skoog solid media, with a small glass vial containing Hoagland media inserted into the jar. This small vial was inoculated with the specified bacterium and served as the source of bacterial volatiles. This way plants were exposed to mVOCs without having any physical contact with the rhizobacteria.•The procedure allows studying the effect of microbial VOCs on plant growth.•It also allows longer trials, being able to let the plant develop more without space limitation.