Effects of non‐thermal plasma technology on Diaporthe longicolla cultures and mechanisms involved

Abstract

BACKGROUND The Diaporthe/Phomopsis complex (D/P) is a group of soybean seed‐borne fungi. The use of chemical fungicides, either for seed treatment or during the crop cycle, is the most adopted practice for treating fungal diseases caused by this complex. Worldwide, there is a search for alternative seed treatments that are less harmful to the environment than chemicals. Non‐thermal plasma (NTP) is a novel seed treatment technology for pathogen removal. This research aimed to evaluate the effects of NTP on the in vitro performance of pure cultures of Diaporthe longicolla and elucidate the mechanisms underlying these effects. RESULTS Active D. longicolla mycelium, growing in vitro, was exposed to different NTP treatments, employing a dielectric barrier discharge arrangement with different carrier gases (N2 or O2). Fungal growth, fresh biomass and colony appearance were negatively affected by plasma treatments (TN3 and TO3). Lipid peroxidation and antioxidant activities were higher in plasma‐treated colonies comparison with non‐exposed colonies (control). Fungal asexual spores (conidia) were also exposed to NTP, showing high susceptibility. CONCLUSION Exposure of D. longicolla colonies to NTP severely compromised fungal biology. Ozone production during treatment and lipid peroxidation of fungal cell membranes appeared to be involved in the observed effects. © 2020 Society of Chemical Industry

Entering the plasma agriculture field: An attempt to standardize protocols for plasma treatment of seeds

“…Changes in germination or plant growth parameters have been observed with all the gases listed above. For example, helium was used in References [30,35,36,68,78,82,84,94], argon in References [22,23,33,38,60,62,109,111,117,128,133], air in References [11,36,41,48,51,58,61,79,80,90], and nitrogen in References [9,30,61,69,85,95,99] Various gases [24,118] or mixtures of gases are used in References [50,77,86,92] while nitrogen or oxygen [88,120] is used as a carrier gas in References [13,64]. Evidently, the reactive species composition differs for different ratios of oxygen and nitrogen, as shown by Tomekova et al …”

“…[ 9,43,76,90 ] In a corona, plasma is formed at the high‐voltage tip of a sharp edge and forms diffuse plasma toward the ground electrode; corona arrays [ 43,91,92 ] have also been combined in a VDBD with a needle‐to‐plane matrix electrode. [ 13,60–64 ]…”

“…[ 9,21,28,31,42,47,48,60,72,89,91,92 ] Thermocouples, [ 9,28,89 ] fiber‐optic probes, [ 22,23,57 ] and/or infrared imaging cameras can be used to determine surface and seed temperatures. [ 20,57,60,99 ] The gas composition of the plasma can be monitored by a relative humidity (RH) probe [ 22 ] ; gas sensors [ 9,20,51,69 ] can be used for and ozone measurements; optical emission spectroscopy of the plasma can be performed for qualitative or quantitative measurements of electronically excited species [ 10,22,40,48,51,59,61,91,95,100 ] ; Fourier‐transform infrared (FTIR) absorption spectroscopy [ 29,49,50,59,61 ] (measured directly within the FTIR sample compartment if possible) [ 26,42,53 ] can be performed for measurements of nonhomopolar molecules; and UV absorption spectroscopy [ 19,20,64,91 ] and/or laser‐induced fluorescence measurements of specific radicals can be performed. [ 18,46,67,91 ] It is recommended to provide a diagram indicating where and how readings are taken in published studies.…”

“…[21,41,41,[47][48][49][50][51]55,56,58,63,104,119,129,130] However, because a precise time-dependent measurement of the fast current pulses in DBDs is generally difficult, the dissipated discharge power is more conveniently calculated from the DBD voltage and the cycleaveraged DBD current using the charge measured on a series capacitor: The enclosed area of the charge-voltage diagram, known as a Lissajous figure whose locus repeats for each cycle, [131] gives the energy per AC period. Examples of Lissajous figure calculations can be found in References [11,15,19,19,27,45,51,53,62,64,116,131]. For a given electrode configuration and peak voltage, the power is proportional to the frequency if the energy per cycle remains constant.…”

“…[9,43,76,90] In a corona, plasma is formed at the high-voltage tip of a sharp edge and forms diffuse plasma toward the ground electrode; corona arrays [43,91,92] have also been combined in a VDBD with a needle-to-plane matrix electrode. [13,[60][61][62][63][64] These different types of plasma device can be expected to yield different effects for seed treatment in plasma agriculture, although only a few direct comparisons have been made. For example, different results for the germination and measurements of sprouts when comparing gliding arc, a corona array, a downstream microwave plasma, and a diffuse coplanar SDBD were evaluated by Sera et al [43] They found that the SDBD required shorter exposure times due to its high plasma density relative to other devices.…”