A soil bacterium can shape belowground interactions between maize, herbivores and entomopathogenic nematodes

Abstract

Entomopathogenic nematodes (EPN) use odor cues to locate and infect their insect hosts in the soil, making them an important tool in sustainable management of agricultural insect pests. However, very little information is available on the role of soil bacteria in mediating belowground interactions between plants, herbivores and the EPN. In this study, a maize-herbivore-entomopathogenic nematode complex was used to investigate the effect of plant root colonization by a soil bacterium on belowground tritrophic interactions. The impact of maize root colonization by Bacillus pumilus strain INR-7 on the preference of the EPN, Heterorhabditis bacteriophora was tested in four arm olfactometer bioassays in the presence or absence of the root herbivore Diabrotica virgifera LeConte (Coleoptera: Chrysomelidae). Plant volatiles were collected for profile characterization. Further preference assays were performed using plant volatile extracts and synthetic volatiles. In the absence of the root herbivore, the nematodes were attracted to maize roots whose seeds were coated with dead and living bacteria. In the presence of the herbivore, the nematodes selectively oriented towards infested plants whose seeds were treated with B. pumilus strain INR-7 than dead bacteria treated, untreated plants or sunshine sand mix. In contrast, plant volatile extracts or pure compounds did not reproduce the observed behavior. The study showed that bacterial coating of maize seeds with the tested strain may play an important role in shaping belowground tritrophic interactions through mechanisms that would require further investigations. The potential of B. pumilus strain INR-7 integration in maize rootworm management program is discussed.