Characterization of Rhizoctonia cerealis sensitivity to thifluzamide in China

Abstract

Wheat sharp eyespot (WSE) caused by Rhizoctonia cerealis is a major soilborne fungal pathogen in winter wheat in China. The succinate dehydrogenase inhibitor (SDHI) fungicide thifluzamide has significant fungicidal activity against Rhizoctonia spp., but the sensitivity of R. cerealis and the efficacy of thifluzamide for the control of R. cerealis are unknown. One-hundred sixty-seven R. cerealis isolates were collected from Jiangsu Province in China, and their sensitivity to thifluzamide was determined in vitro. Of these, seventy-seven isolates collected in 1984 and 2001 from 53 fields with no previous history of exposure to SDHI fungicides were used to establish baseline sensitivity. Baseline EC50 (effective concentration that results in 50% of mycelial growth inhibition) values for thifluzamide ranged from 0.0145 to 0.0764 (0.0370 ± 0.0014) mg l−1. The EC50 values for thifluzamide inhibition in the other 90 isolates collected in 2008, 2010 and 2013 from 62 fields with a history of likely exposure to SDHI fungicides, ranged from 0.0178 to 0.0889 (0.0382 ± 0.0015) mg l−1. The mean EC50 value of the baseline isolates was not significanty different than the mean EC50 value of the isolates collected after the introduction of the fungicide. In field trials in 2013 and 2014, the efficacy of thifluzamide applied at the late tillering stage [Zadok's growthstage (GS) 29)] at a concentration of 72.0 g a.i. ha−1 ranged from 75.8% to 91.7%. The efficacy of thifluzamide applied at the early stem elongation stage (GS 30) at a concentration of 72.0 g a.i. ha−1 ranged from 77.9% to 86.3%. The efficacy of jinggangmycin, a fungicide extensively used in China, ranged from 34.3% to 73.1% during 2012–2014. These results suggest that thifluzamide is very effective against WSE and could be a good alternative fungicide to jinggangmycin.