Integrated control strategies against the late crown and root rot of sugar beet (Rhizoctonia solani)
R. solani AG 2-2IIIB on sugar beet
Since the early ‘90s the late crown and root rot of sugar beet (Rhizoctonia solani AG2-2IIIB) causes yield and quality losses in German sugar beet growing areas. Besides the broad host range of the soilborne fungus, its occurrence in patches and the absence of chemical control products are the main reasons for the difficulties in controlling R. solani. It is known that R. solani occurs ubiquitously and the onset of the disease is strongly influenced by external factors like crop rotation, soil structure, soil moisture and temperature.
The aim of the project is to study the complex interaction of these factors using novel geo-referenced data analysis as well as molecular methods.
This three year large-scale research project is carried out in cooperation with the Institute of Sugar Beet Research in Göttingen (IFZ), the working group for promotion of sugar beet growing Regensburg (ARGE), and the German Weather Service (DWD). The project is funded by the Bavarian State Ministry of Food, Agriculture and Forests and the Südzucker AG. The project is split up in sub-projects. The sub-projects carried out by the Bavarian State Research Center (LfL) will be introduced in the following.
Description of the sub-projects
Sub-project 1: Field study for the identification of Rhizoctonia risk areas by linkage of geo-referenced, weather, crop rotation and white sugar yield data
The aim of sub-project 1 is to identify risk factors for Rhizoctonia root rot disease in a large scale field study. For this purpose available geo-referenced data, weather data and crop rotation data of fields with sugar beet growing were evaluated for nine Southern Bavarian Districts. (supervised by LfL/IAB1a)
Sub-project 2: Quantification of Rhizoctonia soil inoculum densities using the quinoa-qPCR assay
The R. solani AG2-2IIIB specific molecular quantification method (quinoa-qPCR assay) established at LfL/IPS 3c will be used for real-time monitoring of the Rhizoctonia inoculum potential in soil. In sub-project 1 the quinoa-qPCR assay will be used for measuring the Rhizoctonia soil densities in identified Rhizoctonia risk areas. In sub-projects 3 and 4 the Quinoa-qPCR assay will be used for monitoring Rhizoctonia concentrations in the soil during experiments in the field and the growth chamber (phytotron). (supervised by LfL/IPS3c)
Sub-project 3: Investigations on the interaction between environmental factors, soil tillage strategies and the Rhizoctonia soil inoculum potential
Evaluation of hypotheses about the influence of physical and chemical soil properties (e.g. soil temperature, soil structure and soil moisture, variation due to different soil tillage, soil density and plant residues in the soil) on the Rhizoctonia soil inoculum potential (quinoa-qPCR assay, indicator plant assay) by conducting experiments in the field and in the growth chamber (phytotron). (supervised by LfL/IPS3c, IFZ and ARGE)
Sub-project 3A: Effect of soil structure and weather conditions on the Rhizoctonia inoculum potential in soil and infestation rates of sugar beets with R. solani
Sub-project 3B: Investigations on the relationship between soil density, soil moisture, soil organic matter and the Rhizoctonia soil inoculum potential in a controlled environment (phytotron)
Supplementary to the field trials (sub-project 3A) first tentative tests will be conducted in order to study the interaction between soil density, soil moisture, soil organic matter and the Rhizoctonia soil inoculum potential in a controlled environment in the phytotron. The indicator plant assay and the quinoa-qPCR assay will be used to monitor changes in the inoculum potential of R. solani in soil. Because of the dependence of field tests on year-specific environment variations, this sub-project studies to what extent experiments can be simulated under standardized environment in the phytotron. The advantage would be to provide results for the population dynamic of R. solani all-season and regardless of weather conditions.
Sub-project 4: Investigations on the impact of increased cultivation of crops like soybean and sorghum on the Rhizoctonia soil inoculum potential during crop rotation cycles with sugar beet
This sub-project studies in line with a three year field test, the impact of energy and protein crops like maize, sorghum, soybean and wheat as part of crop rotation sequence patterns with sugar beet on the soil inoculum density of R. solani AG2-2IIIB and the incidence of the Rhizoctonia root rot disease in all crops investigated. (supervised by LfL/IPS 3c and ARGE)
Typical R. solani AG2-2IIIB symptoms
round patches with damaged plants in beet fields
crops with higher tendency to lodge
reduction of root tissue, damaged prop roots and typical Rhizoctonia “eyespot” on the stem
crops with higher tendency to lodge
soybean field in crop rotation with sugar beet
reddish brown, sunken lesions on hypocotyl
‘Girth scab’ of sugar beet is a characteristic disease of mature sugar beet roots. It is, however, often detected not before harvest: upper parts of the plants, including the leaves will remain almost entirely healthy, while beet roots below soil line are typically scabby, irregularly fissured, darkly discoloured and covered with large patchy and suberised necroses.