Suppression of Belowground Volatiles in Maize Depends on Cover Crop Legacy and Genotype

Volatile organic compounds are important chemical signals involved in plant-insect interactions. In recent decades, volatiles have been used in many agricultural applications to help control crop pests, but fewer applications have been developed for belowground pests despite volatile signaling and olfactory cues being crucial for orientation and communication of belowground organisms. Volatile signals also depend heavily on soil characteristics which influence both production and diffusion of these volatile compounds. Cover cropping is one agricultural practice that significantly alters soil properties and has been shown to help control certain insect pests, but there is insufficient data on how cover cropping can affect belowground volatile production and recognition. In this study we explored constitutive and root herbivore induced total belowground volatile emissions in two commercial cultivars of maize (Zea mays L.) planted after different cover crop treatments as well as entomopathogenic nematode (EPN) foraging behavior toward plant cues. Contrary to expectation, we found that volatile emission was significantly reduced in response to herbivore feeding and this response was stronger when maize was planted after certain cover crops. In addition, infective juvenile EPN moved equally toward both herbivore-infested and control plants and were not affected by cover crop treatment. Our results suggest that plant responses to insect damage do not always result in adaptive indirect defenses: in some contexts, herbivores may actually reduce their visibility to natural enemies. Moreover, the plasticity and intensity of these responses depend on both plant genotype and soil legacy.