An interview with Professor Verreet of the Christian-Albrechts-University in Kiel, Germany.
June 30th, 2015
Professor Verreet is Head of the Department of Phytopathology at the Christian-Albrechts-University in Kiel, Germany. His research and teaching focuses on the epidemiology of fungal pathogens of major crops and their integrated control. Professor Verreet`s achievements include developing Integrated Pest Management (IPM) models for major crops by analyzing several multi-annual and supra-regional case studies on epidemic and damage dynamics, resulting in functional control thresholds. In 2014, the American Phytopathological Society (APS) recognized Prof. Verreet with its “Excellence in Teaching” award for the production of short videos on the biology of fungal pathogens. We spoke with Professor Verreet about his view on the relevance of Rhizoctonia in European corn and wheat.
In the past, you worked mainly on foliar pathogens such as Septoria and Fusarium. Your current project focus has changed to a below-ground pathogen. What interests you in this research?
Seed and soilborne pathogens are the least studied fungi in plant pathology since the damage they cause is not directly visual. Yet, I believe that soilborne pathogens are globally the economically most relevant pathogens. The prevalence of Rhizoctonia we observed in this study in European soils and corn plants was an eye-opener for me. The fact that Rhizoctonia is plurivor – meaning it has many host plants and numerous anastomosis groups – makes it a complex and challenging field of research.
What insight have you gained from your on-going Rhizoctonia survey?
This project is part of the PhD thesis carried out by my student Mrs. Gesine Thomsen. In 2014, we analyzed soil samples and corn plants of 25 locations in Germany, 30 locations in France and two locations in Switzerland. Disease pressure and the presence of the Rhizoctonia solani anastomosis groups AG 1-1 A, AG 1-1 B and AG 2-2 IIIB, and R. cerealis CAG 1/AG-D, were determined for these samples using Q-PCR. For 84% of the locations, at least one of the above-mentioned pathogens was observed. AG 2-2 IIIB and R. cerealis showed the highest prevalence, both in terms of detection frequency and disease severity. Additionally, we analyzed 17 sites in Schleswig-Holstein (Germany) – 10 sites with corn plants and 7 sites with wheat plants. The soil samples were subdivided in three soil depths (5, 15 and 30 cm). The detection frequency of the above-mentioned pathogens was 100%, with the highest amount of Rhizoctonia inoculum detected at 15 cm depth.
With this study planned as a 3 years project, do you expect differences between years?
With respect to the inoculum present, I do not expect differences between years. But the interaction between the plant and the pathogen present is likely to vary. The change from a saprophytic stage to a pathogenic stage of Rhizoctonia is highly influenced by weather conditions. This year we had a more wet and cold spring in northern Germany, which resulted in very high Rhizoctonia infections.
Are some locations more prone to Rhizoctonia infections?
When sampling, we captured all available information on previous crop and soil preparation. In analysing our data, we found a higher level of Rhizoctonia in the plant material when there had been a narrow crop rotation or even monoculture of corn. As always, integrated pest management using all phytosanitary measures available – such as ploughing and a wider crop rotation combined with a seed dressing – is the most efficient way of protecting our crops.
Were there surprises or unexpected results?
To start with, I did not expect such a high level of Rhizoctonia – especially R. cerealis in corn plants. We have also detected rather high levels of Rhizoctonia DNA even at harvest in the ear of wheat plants. I would like to have a closer look at the relevance of this Rhizoctonia presence for yield. In order to do so, dedicated trials need to be conducted under controlled conditions. We know from a previous project on Rhizoctonia in sugar beets that the presence of Rhizoctonia is correlated with changed chemical and physical parameters of soil. It is also influenced by the soil type and soil compaction. Preliminary results additionally show a correlation between pH and Rhizoctonia infection in corn: higher infections, higher pH. You can see that there are several aspects we would like to understand better about the behaviour, the pathogenesis, the damage potential, and the epidemiology of Rhizoctonia in corn and wheat in Europe.
Additional information on the Root Health Knowledge Pool
Rhizoctonia short video produced by Prof. Verreet
Preliminary study results as shared during the 2015 European Root Health Forum (Berlin, Germany):
Professor Verreet was interviewed by Dr. Melanie Goll, Technical Innovation Manager, Syngenta. Melanie holds a Ph.D. in plant pathology and focuses on seed treatment development, especially fungicides and nematicides.