Priming negatively affects feeding behaviour and aphid biomass of Rhopalosiphum padi on barley

Plants have developed numerous strategies for responding to abiotic and biotic stresses. In particular, the microbiota surrounding plants may have a positive effect on plant stress responses. One is the reaction to rhizobacteria, which can lead to induced systemic resistance. Gram-negative soil bacteria that produce N-acyl homoserine lactones (AHL), for example, Ensifer meliloti, induce a primed state in plants that is part of the inducible resistance phenomenon. Observing Rhopalosiphum padi feeding behaviour on a priming sensitive barley genotype, treated with the AHL-producing E. meliloti strain expR + ch, using electrical penetration graph technique showed decreased ingestion of food. Aphids appear to overcome this effect within the eight-hour observation period, possibly explaining the absence of differences of reproduction. Reproduction was observed for a period of 14 days on primed and control-treated plants. Long-term observations over a period of 40 days after aphid infestation showed a lower aphid biomass in contrast to a control group, interpreted as delayed population growth, and an increase in the biomass of barley plants. Priming-related genotypic effects of the defence response to aphids were observed, with no beneficial effects on the plant genotype when its sensitivity to priming was low. Previously, an AHL-priming sensitive barley genotype showed enhanced resistance against fungi when primed with the expR + ch strain of E. meliloti. The present study reports the same effect against R. padi. These findings suggest that sensitivity to AHL-priming may represent a new approach for plant breeding, targeting multiple pests in parallel by induced plant resistance.