Wormy Warning? Root‐Knot Nematode Infection Reduces Host Fitness but Does Not Affect Neighbouring Conspecific Plants

Abstract

In the animal kingdom, natural enemies such as predators and parasites can influence their hosts through both direct consumptive effects (CEs) resulting from death or injury, with indirect non‐consumptive effects (NCEs) arising from trait changes induced by the risk of attack. Although parasite‐induced NCEs have been increasingly documented in animals, their potential occurrence in plant–parasite interactions remains largely unexplored. We investigated whether bean plants (Phaseolus vulgaris) infected with the root‐knot nematode (Meloidogyne hapla) could induce trait changes in neighbouring uninfected conspecifics. Potted ‘signaller’ bean plants that were either nematode‐exposed or not were paired with unexposed ‘receiver’ plants able to perceive cues through both soil and air or just air. We measured plant height change, root‐to‐shoot biomass ratio, bean production and total plant biomass. Nematode‐exposed signallers showed reduced survival, root‐to‐shoot biomass ratio and total biomass compared with unexposed signallers. However, signaller plant exposure status had no detectable effect on any measured trait of neighbouring receiver plants. Receiver ability to perceive both soil‐ and airborne cues also had no overall effect, nor was there a significant interaction between cue type and signaller exposure status. Under the conditions tested, the costs of M. hapla infection appeared largely limited to direct effects on infected plants, with no evidence that infected individuals induce costly trait responses in neighbouring conspecifics. Future studies examining other host species, environmental conditions and interactions with plant pathogens or herbivores will help clarify the potential for plant‐parasitic nematodes to generate indirect effects within plant populations.