Priming of indirect defence responses in maize is shown to be genotype-specific

Priming is an induced defence mechanism in which plants that have been exposed to elicitors, such as herbivore-induced plant volatiles (HIPVs), go into an alert state with faster and stronger responses against a future biotic challenge. This study evaluated whether HIPVs emitted by maize genotypes after herbivory by fall armyworm (Spodoptera frugiperda) larvae could prime neighbouring maize plants for an enhanced indirect defence response, and if priming was consistent across different genotypes. Two genotypes were selected based on their differences in HIPV emission: Sintético Spodoptera (SS), a relatively high emitter of HIPVs, and L3, a relatively low emitter of HIPVs. SS plants that were previously exposed to SS HIPVs initiated earlier and enhanced volatile production upon larval challenge, compared to SS plants that were previously exposed to SS undamaged plant volatiles. In addition, SS plants exposed to SS HIPVs and then to larval challenge attracted an egg parasitoid, Telenomus remus, at an earlier stage than SS plants that were only subjected to larval challenge, indicating a priming effect. There was no evidence of a priming response by L3 plants that were previously exposed to L3 or SS HIPVs. When comparing the gene expression of HIPV-exposed and undamaged plant volatile (UDV)-exposed plants, jasmonate-induced protein GRMZM2G05154 and UDP-glucosyltransferase bx8 genes related to the biosynthesis of DIBOA-Glu were upregulated. These data indicate that priming by HIPVs enhances indirect defence in maize plants as reported by other studies, and provide new information showing that the priming effect can be genotype-specific.