Elicitation of resistance to bacterial canker of stone fruits by humic and fulvic acids (glucohumates): a cDNA-AFLP-dHPLC approach

Bacterial leaf/fruit spot and canker of stone fruits, caused by Xanthomonas arboricola pv. pruni is a challenging disease in Italian orchards. In recent years, novel molecules such as biostimulants or/and resistance-inducers have been developed and used to implement an effective Integrated Pest Management. An extensive study in vitro, in glasshouse and in a peach orchard was carried out to verify the efficacy of commercial glucohumates to control bacterial spot/canker outbreaks and to understand their mode of action. A transcriptomic approach was implemented to study the complex transcriptional changes that these biomolecules may possibly elicit in the plant-pathogen interaction. The cDNA-AFLP analysis of differential gene expression in treated plant tissue was made. Discrimination of differentially expressed sequences was made with denaturing High Performance Liquid Chromatography (dHPLC), and functional annotation of such transcripts was assigned based on similarity search on public genome databases. The results highlighted the activity of glucohumates in controlling Xanthomonas arboricola pv. pruni both in vitro and in vivo. Beneficial effects of humic substances towards this pathogen were confirmed by a significant disease reduction (up to 78%) in the commercial orchard. On the other hand, cDNA-AFLPdHPLC analysis allowed the collection of fourteen up-regulated transcript-derived fragments belonging to peach genes and putatively involved in the defence response. In particular, the activation of these genes within 24 h after treatment supposedly triggered the early-induced resistance, notoriously involved in maintaining a protection state in plants against biotic stresses.