Survey on the prevalence of Rhizoctonia spp. in European soils and determination of the baseline sensitivity towards sedaxane

The prevalence of Rhizoctonia spp. in European soils was determined by analysing soil samples from 282 locations. Rhizoctonia spp. were found in 68% of these samples from France, Germany, the UK, Poland, Italy, Spain, Hungary and the Czech Republic. Samples from 136 locations were further analysed by pyrosequencing. Seventy‐six percent of the isolates were Rhizoctonia solani and 24% binucleate Rhizoctonia spp. Rhizoctonia solani anastomosis group (AG) 5 was detected most frequently (25%), followed by AG 9 (16%) and AG 4 (13%). For the binucleate Rhizoctonia spp., AG E was most prevalent (13%). Rhizoctonia cerealis was not detected in soil samples. Soil type or cropping history had no effect on the type of Rhizoctonia observed. Rhizoctonia solani AG 5 was the most frequently detected AG irrespective of the previous crop. The spectrum of AGs detected was similar for France, Germany and Poland but was significantly different for the UK (P = 0·0016). Finally, the baseline sensitivity towards sedaxane, a new active ingredient for seed treatment, was analysed for all isolates. The results indicate a low baseline sensitivity (average EC₅₀ of 0·028 p.p.m.) for all Rhizoctonia AGs. No difference in sensitivity was observed with the isolates obtained from different countries.