A New Spore Precipitator with Polarized Dielectric Insulators for Physical Control of Tomato Powdery Mildew

Abstract

In an attempt to physically protect greenhouse tomato plants from the powdery mildew fungus Oidium neolycopersici, we developed a new electrostatic spore precipitator in which a copper wire conductor is linked to an electrostatic generator and covered with a transparent acrylic cylinder (insulator). The conductor was negatively charged by the generator, and the electrostatic field created by the conductor was used to dielectrically polarize the insulator cylinder. The dielectrically polarized cylinder also produced an electrostatic force without a spark discharge. This force was directly proportional to the potential applied to the conductor and was used to attract conidia of the pathogen. The efficacy of this spore precipitator in protecting hydroponically cultured tomato plants from powdery mildew was evaluated in the greenhouse. The hydroponic culture troughs were covered with a cubic frame installed with the spore precipitator, and the disease progress on precipitator-guarded and unguarded seedlings was traced after the conidia were disseminated mechanically from inoculum on tomato plants. Seedlings in the guarded troughs remained uninfected during the entire experiment, in spite of rapid spread of the disease to all leaves of the unguarded seedlings.

Natural woody plant, Mallotus japonicus, as an ecological partner to transfer different pathotypic conidia of Oidium neolycopersici to greenhouse tomatoes

“…We targeted conidiophores for microscopic observations, because of the easy and rapid detection of conidial pseudochains on them (Oichi et al 2004(Oichi et al , 2006. Pseudochain formation is common in the tomato powdery mildew pathogens (Jones et al 2001;Kiss et al 2001), and the number of conidia in the pseudochain is inherited (Oichi et al 2006;Nonomura et al 2009). …”

Practical Application of an Electric Field Screen to an Exclusion of Flying Insect Pests and Airborne Fungal Conidia from Greenhouses with a Good Air Penetration

“…The outer net surfaces possessed no charge and were safe to touch. Insulation of the charged ICWs suppressed the electric current through arc discharge (Matsuda et al, 2006(Matsuda et al, , 2011Tanaka et al, 2008). If an insulator sleeve was to be accidentally broken, the grounded nets would act as a safety device to direct electric current from the charged ICWs to a ground.…”

“…To waterproof the screen, the generator and the electric wires connecting the ICWs to the generator were placed inside the frame and sealed with silicon resin. The ICWs were negatively charged to dielectrically polarise the ICW insulator sleeve; the outer surface was negatively charged and the inner conductor-wire surface was positively charged (Matsuda et al, 2006). The negative surface charge of the ICWs polarised (electrostatically induced) the grounded nets (conductor), creating the opposite surface charge on the ICW-side net surfaces.…”

“…This electrostatic method was devised initially to collect mature conidia on conidiophores of powdery mildews (Moriura et al, 2006a(Moriura et al, , 2006bNonomura et al, 2009). It has been further developed as a spore-precipitation screen for tomato powdery mildew (Matsuda et al, 2006;Shimizu et al, 2007) and an insect-exclusion screen for whiteflies (Tanaka et al, 2008), cigarette beetles, and vinegar flies (a warehouse pest) (Matsuda et al, 2011). The first electrostatic spore precipitator was a screen that created a non-uniform electric field around insulated copper conductor wires arranged in parallel (Matsuda et al, 2006).…”

“…It has been further developed as a spore-precipitation screen for tomato powdery mildew (Matsuda et al, 2006;Shimizu et al, 2007) and an insect-exclusion screen for whiteflies (Tanaka et al, 2008), cigarette beetles, and vinegar flies (a warehouse pest) (Matsuda et al, 2011). The first electrostatic spore precipitator was a screen that created a non-uniform electric field around insulated copper conductor wires arranged in parallel (Matsuda et al, 2006). The electric field generated an electrostatic force that attracted fungal conidia entering the field.…”