Efficacy of Essential Oil Vapours in Reducing Postharvest Rots and Effect on the Fruit Mycobiome of Nectarines

Abstract

Nectarines can be affected by many diseases, resulting in significant production losses. Natural products, such as essential oils (EOs), are promising alternatives to pesticides to control storage rots. This work aimed to test the efficacy of biofumigation with EOs in the control of nectarine postharvest diseases while also evaluating the effect on the quality parameters (firmness, total soluble solids, and titratable acidity) and on the fruit fungal microbiome. Basil, fennel, lemon, oregano, and thyme EOs were first tested in vitro at 0.1, 0.5, and 1.0% concentrations to evaluate their inhibition activity against Monilinia fructicola. Subsequently, an in vivo screening trial was performed by treating nectarines inoculated with M. fructicola, with the five EOs at 2.0% concentration by biofumigation, performed using slow-release diffusers placed inside the storage cabinets. Fennel, lemon, and basil EOs were the most effective after storage and were selected to be tested in efficacy trials using naturally infected nectarines. After 28 days of storage, all treatments showed a significant rot reduction compared to the untreated control. Additionally, no evident phytotoxic effects were observed on the treated fruits. EO vapors did not affect the overall quality of the fruits but showed a positive effect in reducing firmness loss. Metabarcoding analysis showed a significant impact of tissue, treatment, and sampling time on the fruit microbiome composition. Treatments were able to reduce the abundance of Monilinia spp., but basil EO favored a significant increase in Penicillium spp. Moreover, the abundance of other fungal genera was found to be modified.

Keywords: Prunus persica; biofumigation; brown rot; metabarcoding; stone fruit.

Figure 1

Rot incidence (%) ± standard error (SE) on nectarines treated with essential oil biofumigation stored at 1 ± 1 °C for 14 days and kept in shelf life at 20 ± 1 °C for 7 days. Values at the same time point, followed by the same letter, are not statistically different by Duncan’s multiple range test (p < 0.05).

Figure 2

Rot incidence (%) ± standard error (SE) on nectarines treated with essential oil biofumigation stored at 1 ± 1 °C for 28 days and kept in shelf life at 20 ± 1 °C for 5 days. Values at the same time point, followed by the same letter, are not statistically different by Duncan’s multiple range test (p < 0.05).

Figure 3

Box and whisker plots of alpha diversity values of analyzed microbial communities based on tissue, sampling time point, and treatment group. The middle line of each box coincides with the mean, while the upper and lower box bounds are placed at one standard deviation from the mean. Whiskers above and below the box extend to the highest and lowest values of their respective group. Letters above each plot indicate the significance group of that plot. Comparison of sample groups and assignation to significance groups was performed by means of a Kruskal–Wallis test followed by a Dunn post hoc test, with a q-value (FDR-adjusted p-value) rejection threshold set at 0.05.

Figure 4

PCoA plot of the robust Aitchison distance matrix values calculated on analyzed samples. Percentage values represented on the main axes indicate explained variance associated with each principal component. Point shape indicates the sampling time point, while color indicates the associated treatments. Finally, group ellipses indicate the associated tissue.

Figure 5

Taxa compositions of epiphytic (upper side) and endophytic (lower side) fungal communities. The “Other” category includes all taxa with less than 1% relative presence in all considered groups.