No abstract

Fungal diseases seriously affect agricultural production and the food industry. Crop protection is usually achieved by synthetic fungicides, therefore more sustainable and innovative technologies are increasingly required. the atmospheric pressure low-temperature plasma is a novel suitable measure. We report on the effect of plasma treatment on phytopathogenic fungi causing quantitative and qualitative losses of products both in the field and postharvest. We focus our attention on the in vitro direct inhibitory effect of non-contact Surface Dielectric Barrier Discharge on conidia germination of Botrytis cinerea, Monilinia fructicola, Aspergillus carbonarius and Alternaria alternata. A few minutes of treatment was required to completely inactivate the fungi on an artificial medium. Morphological analysis of spores by Scanning electron Microscopy suggests that the main mechanism is plasma etching due to Reactive oxygen Species or UV radiation. Spectroscopic analysis of plasma generated in humid air gives the hint that the rotational temperature of gas should not play a relevant role being very close to room temperature. In vivo experiments on artificially inoculated cherry fruits demonstrated that inactivation of fungal spores by the direct inhibitory effect of plasma extend their shelf life. Pretreatment of fruits before inoculation improve the resistance to infections maybe by activating defense responses in plant tissues.

Basil (Ocimum basilicum) seeds were treated for different exposure times with a non-equilibrium plasma produced by a volume dielectric barrier discharge in humid air at atmospheric pressure. Plasma treatment did not change the seed structure and morphology, as visualized by high-resolution computed x-ray microtomography. A faster and higher germination rate was observed with plasma treatment of 1 and 3 min. Plantlets grown in sand, after both 2 and 3 weeks, showed a more developed root apparatus and better biometric parameters, compared to plants developing from non-treated seeds. After the plasma treatment, internal redistribution of macro and micronutrients was observed by using micro x-ray fluorescence spectroscopy. In particular P, K and Mg concentrated in the radicle, moving from the endosperm and cotyledons, while Zn, initially concentrated in specific tissues of the cotyledon, appeared more homogeneously distributed inside the whole seed after the plasma treatment. Significant variations in electrical impedance spectra were also observed after plasma treatment. This element redistribution in the seed was caused by the intense electrical field generated by the volume dielectric barrier discharge plasma, causing a movement of important micro and macronutrients from the storage regions of the seed towards the radicle tissues. This ion movement could explain the observed faster germination of the plasma-treated seeds. Indeed, such movement of ions is similar to what is generally observed in seed tissues during germination. The plasma treatment therefore somehow anticipates and implements the mobilization of key nutrients towards the radicle, resulting in faster and higher germination of the seeds as well as improved characteristics of the basil plantlet, especially at the root level.