An ozone‐generative electrostatic spore precipitator was developed to protect nursery‐stage seedlings of tomato from both airborne conidia of powdery mildew ( Oidium neolycopersici ) and root‐infecting pathogen propagules of bacterial wilt ( Ralstonia solanacearum ) and fusarium crown and root rot ( Fusarium oxysporum f.sp. radicis‐lycopersici ). The device was a cylindrical electrostatic spore precipitator (S2 cylinder) in which a positively charged straight conductor wire insulated with a transparent acrylic cylinder originated from a spore‐precipitation cylinder (S1 cylinder) designed to physically control airborne conidia of tomato powdery mildew in greenhouses. The S2 cylinder consisted of two sites for conidial attraction and ozone production. The site for ozone production was located at the end of the cylinder, where an earthed copper conductor ring (as a cathode) was attached to the edge of the cylinder, responding to the anodal tip of a positively charged central conductor wire. Distinct types of discharge (corona, corona‐streamer, streamer and arc discharge) occurred between the two electrodes and were dependant on the voltages applied to the wire and the distances between the electrodes. The highest ozone production was observed through streamer discharge. The remaining portion of the S2 cylinder, which was dielectrically polarized by a positively charged wire, created a non‐uniform electric field outside the cylinder to attract conidia that came into the generated field. Hydroponic culture troughs to raise tomato seedlings in a nursery greenhouse were paralleled with S2 cylinders. The aim was to control rhizosphere pathogens R. solanacearum and F. oxysporum f.sp. radicis‐lycopersici and to prevent them entering the hydroponic system during cultivation, while at the same time trapping O. neolycopersici conidia in the spaces between the cylinders. The results indicated that susceptible tomato plants in culture troughs attached to the S2 cylinders remained uninfected by both rhizosphere and aerial pathogens throughout the experimental period (2 and 3 weeks, respectively). This suggests that the present system will enable the dual control of both these pathogens in hydroponic systems in greenhouses.

A total of 26Ampelomycesstrains were isolated from mycelia of six different powdery mildew species that naturally infected their host plants in Japan. These were characterized based on morphological characteristics and sequences of ribosomal DNA internal transcribed spacer (rDNA-ITS) regions and actin gene (ACT) fragments. Collected strains represented six different genotypes and were accommodated in three different clades of the genusAmpelomyces. Morphology of the strains agreed with that of otherAmpelomycesstrains, but none of the examined characters were associated with any groups identified in the genetic analysis. Five powdery mildew species were inoculated with eight selectedAmpelomycesstrains to study their mycoparasitic activity. In the inoculation experiments, allAmpelomycesstrains successfully infected all tested powdery mildew species, and showed no significant differences in their mycoparasitic activity as determined by the number ofAmpelomycespycnidia developed in powdery mildew colonies. The mycoparasitic interaction between the eight selectedAmpelomycesstrains and the tomato powdery mildew fungus (Pseudoidium neolycopersicistrain KTP-03) was studied experimentally in the laboratory using digital microscopic technologies. It was documented that the spores of the mycoparasites germinated on tomato leaves and their hyphae penetrated the hyphae ofPs.neolycopersici.Ampelomyceshyphae continued their growth internally, which initiated the atrophy of the powdery mildew conidiophores 5 days post inoculation (dpi); caused atrophy 6 dpi; and complete collapse of the parasitized conidiphores 7 dpi.Ampelomycesstrains produced new intracellular pycnidia inPs.neolycopersiciconidiophoresca. 8–10 dpi, whenPs.neolycopersicihyphae were successfully destroyed by the mycoparasitic strain. Mature pycnidia released sporesca. 10–14 dpi, which became the sources of subsequent infections of the intact powdery mildew hyphae. Mature pycnidia contained eachca. 200 to 1,500 spores depending on the mycohost species andAmpelomycesstrain. This is the first detailed analysis ofAmpelomycesstrains isolated in Japan, and the first timing and quantification of mycoparasitism ofPs.neolycopersicion tomato by phylogenetically diverseAmpelomycesstrains using digital microscopic technologies. The developed model system is useful for future biocontrol and ecological studies onAmpelomycesmycoparasites.

Among the mycoparasites, Ampelomyces strains are studied in detail, particularly regarding their use as biocontrol agents (BCAs) of powdery mildew (PM) fungi, including their potential to replace conventional agrochemicals. Ampelomyces strains are characterized morphologically; their ribosomal DNA internal transcribed spacer (rDNA-ITS) regions and actin gene (ACT) fragments were sequenced and their mycoparasitic activity was analyzed. In the interaction between Ampelomyces strains and PM fungi, the spores of the mycoparasites germinate on plant leaves, and their hyphae then penetrate the hyphae of PM fungi. Ampelomyces hyphae continue their growth internally, initiating the atrophy of PM conidiophores and eventually their complete collapse. Following the successful destruction of PM hyphae by Ampelomyces, the mycoparasite produces new intracellular pycnidia in PM conidiophores. The progeny spores released by mature pycnidia become the sources of subsequent infections of intact PM hyphae. As a result, the number of Ampelomyces-inoculated PM colonies gradually declines, and the conidial release of PM colonies is inhibited after the first treatment. Almost all conidiophores of 5- and 10-day-old Ampelomyces-inoculated PM colonies undergo complete atrophy or collapse. Methodological advances and in-depth analyses of the Ampelomyces–PM interaction were recently published. In this review, we summarize the genetic and phylogenetic diversity, the timing of mycoparasitism and pycnidiogenesis, the results of quantitative and visual analyses using electrostatic and digital microscopy technologies, the PM biocontrol potential of Ampelomyces, and the potential commercialization of the mycoparasites. The information provided herein can support further biocontrol and ecological studies of Ampelomyces mycoparasites.