Geographic distribution and disease severity of different Rhizoctonia species pathogenic towards maize in different regions in Germany and France

Abstract

The geographic distribution and DNA-disease severity of the anastomosis groups (AG) 1 IA, AG 1 IB and AG 2-2 IIIB within the teleomorph Thanatephorus cucumeris and R. cerealis (CAG 1, AG-D) within the teleomorph Ceratobasidium cereale, which are known to be pathogenic to maize, were determined by analysing maize roots from different regions with high proportions of maize within the crop rotation in Germany and France in the experimental years 2014 (n = 53) and 2015 (n = 63) using qPCR. For the interpretation of the measured values, a weighted risk index (RI%) was conducted considering cropping history and soil physical properties at the sampled sites. A positive detection of at least one of the tested species was possible in 83% of the samples analysed in both experimental years 2014 and 2015. In 2014, R. cerealis (53%) was most prevalent, while in 2015, AG 2-2 IIIB (70%) shows the highest detection frequency. Regarding the cropping system at the sampled sites, the binucleate Rhizoctonia spp. leads to higher risk indices (RI%) if maize is grown in wide to limited crop rotations with high content of cereals, whereas AG 2-2 IIIB is more present and achieved higher disease severities if maize is grown in monoculture. The other tested members of the teleomorph T. cucumeris, AG 1 IA and AG 1 IB, showed high detection frequencies especially in the experimental year 2014. Regarding the DNA-disease severity, compared to the results of AG 2-2 IIIB, for these two anastomosis groups only a latent infection was observed. Soil type or cropping history had no serve influence on the DNA-disease severity of these two Rhizoctonia spp. in maize.