Controversy about Trichoderma afroharzianum and its role in the ear rot of maize in Europe
In 2018, severe fungal infestations on maize (Zea mays) cobs were observed in several experimental fields in Southern Germany and the causal agent was identified as Trichoderma afroharzianum (Pfordt et al., 2020). The presence of T. afroharzianum causing ear rot symptoms was also detected in a few cases in France and Italy (EPPO RS 2022/087, 2023/194). As this was the first time that a Trichoderma species was associated with a maize disease in Europe, T. afroharzianum was added to the EPPO Alert List.
Trichoderma species are associated with many different substrates such as soil, rhizosphere, decaying plant debris, foliar environment, and some species have been isolated as endophytes. Several strains of Trichoderma have been shown to be beneficial to plants and are being used in agriculture to promote nutrient uptake and plant growth, or to control a wide range of soilborne plant pathogens (e.g. Fusarium, Phytophthora, Rhizoctonia) on various crops.
A recent paper from Trillas et al. (2024) considers that the methodology used in the experiments carried out in Germany was questionable and did not provide sufficient evidence to conclude that T. afroharzianum was an aggressive plant pathogen causing ear rot on maize. In one of their conclusions, the authors wrote that ‘as scientists and according to the International Biocontrol Manufacturers Association (IBMA), it is very important to investigate the real importance of Trichoderma ear rot in Europe and also determine whether Trichoderma is a secondary or a main agent responsible for disease by performing studies under realistic conditions …)’.
No doubt that the debate on this question will continue.
Sources
Trillas I, Segarra G, Avilés M (2024) Is Trichoderma ear rot on maize really a new dangerous plant disease. Frontiers in Agronomy 6, https://doi.org/10.3389/fagro.2024.1386568
Pfordt A, Schiwek S, Karlovsky P, von Tiedemann A (2020) Trichoderma afroharzianum ear rot – A new disease on maize in Europe. Frontiers in Agronomy 2, 547758. https://doi.org/10.3389/fagro.2020.547758
Sanna M, Pugliese M, Gullino ML, Mezzalama M (2022) First report of Trichoderma afroharzianum causing seed rot on maize in Italy. Plant Disease 106(7), 1983. https://doi.org/10.1094/PDIS-12-21-2697-PDN