Plant-derived, nodule-specific cysteine rich peptides as a source of novel biopesticides for controlling citrus greening disease.

Nodule-specific cysteine-rich peptides (NCRs), encoded in the genome of the Mediterranean legume, Medicago truncatula Gaertn. (barrelclover) are known to regulate plant-microbe interactions. A subset of computationally-derived 20-mer peptide fragments from 182 NCR peptides were synthesized to identify those with activity against the unculturable vascular pathogen associated with citrus greening disease, ' Candidatus Liberibacter asiaticus' ( C Las). Grounded in a design of experiments framework, we evaluated the peptides in a screening pipeline involving three distinct assays: a bacterial culture assay with L. crescens , a C Las-infected excised citrus leaf assay, and an assay to evaluate effects on bacterial acquisition by the nymphal stage of hemipteran vector Diaphorina citri . A subset of the 20-mer NCR peptide fragments inhibit both C Las growth in citrus leaves and C Las acquisition by D. citri . Two peptides induced higher levels of D. citri mortality. These findings reveal 20-mer NCR peptides as a new class of plant-derived biopesticide molecules to control citrus greening disease.