Emission of volatile organic compounds during nectarine-Monilinia laxa interaction and its relationship with fruit susceptibility to brown rot

Fruit volatile organic compounds (VOCs) can be emitted by stone fruit in response to biotic stress. One of the main fungal diseases of stone fruit is brown rot, caused by species of Monilinia spp. Hence, we aimed to reveal the most relevant VOCs that participate either in resistance or susceptibility to Monilinia laxa in nectarines. To this aim, we analyzed the VOCs emitted by two developmental stages (immature, one month before harvest; mature, commercial harvest) of two nectarine cultivars, with different susceptibility to M. laxa. Furthermore, we also determined the VOCs profile of M. laxa grown in in vitro culture media based on peach juice. Results elucidated 34 VOCs whose production pattern was different among samples (control and inoculated of both stages and cultivars), being 13 VOCs also emitted by M. laxa culture. A hierarchical analysis and a multivariate analysis exhibited the variations in the VOCs profile of all samples according to their susceptibility to M. laxa, and the suitability of the model to predict the M. laxa disease (91.94% of the total variation). In general, results highlighted i) a group of VOCs, positively correlated with M. laxa disease, that were emitted by visual M. laxa symptomatic tissues (e.g., aldehyde (E,E)- 2,6-nonadienal) and also by M. laxa itself (e.g., terpenoids alpha-muurolene and (E)-beta-ionone), and ii) a group of VOCs, negatively correlated with brown rot disease, that were emitted by tissues with no visual M. laxa symptoms (e.g., ketone butyrolactone and aldehyde (E)- 2-decenal) and also by M. laxa itself (e.g., aldehyde decanal), suggesting an antifungal role of these compounds. Therefore, this study provides putative potential VOCs that not only will help to improve the knowledge of brown rot development on nectarines, but also provides target volatiles that may serve as potential brown rot control compounds.