Fungi Parasitizing Powdery Mildew Fungi: Ampelomyces Strains as Biocontrol Agents against Powdery Mildews

Abstract

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.