Microbe-induced plant volatiles in response to herbivory: Genetics matters

Association of plants with beneficial soil microbes such as plant growth-promoting rhizobacteria can improve plant growth and confer herbivory protection through alterations in the production of plant volatile organic compounds (VOCs). However, much of the current understanding of beneficial soil microbes-conferred herbivore plant protection is based on studies that use only one plant genotype. Yet, crop breeding programs, with every new decade generate new plant genotypes with unique genetic characteristics. This study was conducted to investigate whether PGPR-conferred herbivore protection varies as a function of genotype and microbe community. We used six maize genotypes, representing three decades of crop improvement and two major heterotic groups. Maize plants, inoculated with PGPR, Bacillus altitudinus at planting were grown under greenhouse conditions. Four microbe treatments were used; Bacillus+sterile soil, Bacillus+live soil, live soil and sterile soil. We subjected plants to damage by Helicoverpa zea larvae and collected herbivore-induced volatiles. Volatiles were analyzed and identified using gas chromatography-mass spectrometry. Our results showed that breeding driven manipulations of plant genotype significantly influenced herbivore-induced volatiles. Microbe treatment did not influence the composition of volatiles in response to herbivory.  These results suggests that crop improvement via breeding may entail a hidden cost: disruption of beneficial soil microbes conferred benefits to plants. To fully harness microbial inoculants’ potential to improve plant health and food security, breeding for crops that do not ignore beneficial soil microbes is necessary.