Analysis of Trichoderma as an effective biological control agent against the honey fungus (Armillaria spp.)

Trichoderma is a genus of filamentous fungi with several species widely studied and used as biological control agents (BCAs) in agriculture. With respect to fungal disease control, Trichoderma spp. can use different mechanisms of action, including mycoparasitism, antibiosis, competition and/or activation of plant defences. Armillaria spp. are the causal pathogens of Armillaria root rot (ARR) disease, which is widely distributed and of great economic and environmental importance in agriculture and forestry. ARR can be devastating to plant health, through colonisation and rotting of the root system and collar of the infected plant/tree, which can cause a reduction in yield and eventually death. Armillaria can live as a saprophyte that survives on dead plant material, making eradication of ARR extremely difficult. In an exhaustive analysis of work published to date on the control of Armillaria spp. by Trichoderma spp., using the WoS and Scopus databases, we identified 31 papers. We discuss these reports in light of their key findings, including number of publications per year, the countries where they were published, the journals and the citations obtained so far. Although the vast majority do not identify the mechanism of action involved in control, some describe mycoparasitism, antibiosis, competition or modification of the rhizospheric microbiota as being responsible for effective biological control of the pathogen. Further research into these mechanisms and additional in-depth analysis of less studied or currently unidentified mechanisms, such as the activation of plant defences, would be highly beneficial to our understanding of Trichoderma as a BCA of Armillaria.