Studies on the Rhizoctonia complex in wheat: Relevant anastomosis groups in Europe, symptomology, yield relevance and possibilities of control
As a result of a study on new yield relevant diseases in cereals farmland soil samples originated from different countries across Europe were analyzed for the presence of Rhizoctonia species. It was demonstrated that the anastomosis group 5 (AG5) of R. solani was predominant (Syngenta, unpublished data).
In vitro experiments demonstrated that AG5 -among others- is pathogenic on wheat. In a field study performed in 2011/12 wheat plots were artificially inoculated with Rhizoctonia AG 5 and AG D. It was shown that significant yield losses occur at elevated levels of frost stress in less frost resistant cultivars at moderate or high levels of Rhizoctonia disease incidence. The yield loss was related mainly to a reduction of grain numbers per ear. The Rhizoctonia AG D and AG 5 were used as an isolate mix, therefore competitiveness of both groups can be studied on collected plant samples.
In the present field experiment 2012/13 additionally the effect of a seed dressing will be studied as a possible control measure. The overall aim of the study is to conclude why Rhizoctonia spp. are ubiquitous soil pathogens but are only important to yield under specific conditions.
Therefore, effects of the environmental temperature on the pathogen are studied using different test systems. Different temperature demands of the AG were studied in vitro on the basis of their radial growth. Isolates differing in their temperature growth characteristics were chosen as inoculum in the present field study. This experiment is conducted in the “Göttinger soil warming device”. This device offers mini plots which can be heated according to different climatic scenarios over the whole season. Symptom development and competitiveness of the different Rhizoctonia species and/or types will be studied.