|Amaradasa, Bimal - University Of Nebraska|
|Mccall, David - Virginia Polytechnic Institution & State University|
|Horvath, Brandon - University Of Tennessee|
Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2014
Publication Date: 1/9/2015
Citation: Amaradasa, B.S., Lakshman, D.K., Mccall, D.S., Horvath, B.J. 2015. In vitro fungicide sensitivity of Rhizoctonia isolates collected from turfgrasses. Journal of Environmental Horticulture. 32:126-132.
Interpretive Summary: Plant pathogenic Rhizoctonia isolates are a genetically diverse group of soilborne fungi belonging to several genera, species and anastomosis groups (AGs). Choosing effective fungicides against a specific pathogenic isolate of Rhizoctonia is an important consideration for implementing efficient disease management practices. To determine most efficient fungicides for Rhizoctonia disease control, we tested thirty-six genetically diverse isolates of Rhizoctonia pathogens to three commonly recommended fungicides - triticonazole, iprodione, and pyraclostrobin. Waitea circinata isolates were moderately sensitive to iprodione while isolates of R. solani and binucleate Rhizoctonia-like fungi (BNR) were extremely sensitive. Isolates of AG 2-2IIIB exhibited less sensitivity to triticonazole than AG 1-IB, and W. circinata isolates. Isolates of BNR varied in inhibition of growth by triticonazole, exhibiting extreme to moderate sensitivity. Isolates of W. circinata var zeae were moderately sensitive to pyraclostrobin while most isolates of R. solani and BNR were extremely sensitive. Our study demonstrates the importance of accurately identifying the Rhizoctonia pathogen causing disease symptoms on turfgrass for selecting an effective fungicide.
Technical Abstract: Different Rhizoctonia species and anastomosis groups (AGs) have been reported to show variable sensitivity to various commercial fungicides. Thirty–six isolates of Rhizoctonia collected from turfgrasses were tested in vitro for sensitivity to commercial formulations of iprodione, triticonazole, and pyraclostrobin. Tested isolates represented R. solani AG 1–IB and AG 2–2IIIB; W. circinata varieties zeae (Wcz) and circinata (Wcc); and binucleate Rhizoctonia–like fungi (BNR) from different locations in Virginia and Maryland, USA. Each fungicide was added to PDA medium to obtain concentrations at 0, 0.1, 1, 10 and 100 mg a.i. L–1. A mycelium plug from each isolate was grown on these plates. Fungicide concentration needed for 50% inhibition of radial growth (EC50) was determined for each isolate × fungicide combination. Waitea circinata isolates were moderately sensitive (EC50 = 1 to 10 mg a.i. L–1) to iprodione while isolates of R. solani and BNR were extremely sensitive (EC50 < 1 mg a.i. L–1). Isolates of AG 2–2IIIB exhibited less sensitivity to triticonazole (mean EC50 = 1.26 mg a.i. L–1) than AG 1–IB, and W. circinata (mean EC50 = 0.2, and 0.06 mg a.i. L–1, respectively) isolates. Isolates of BNR varied in inhibition of growth by triticonazole, exhibiting extreme to moderate sensitivity. Isolates of W. circinata were moderately sensitive to pyraclostrobin while most isolates of R. solani and BNR were extremely sensitive. Geographic origin of isolates had no influence on the level of fungicide sensitivity. This study demonstrates the importance of accurately identifying the Rhizoctonia pathogen causing disease symptoms on a turfgrass for choosing an effective fungicide. Additional field tests with these fungicides are needed to determine if in vitro results are repeatable under field conditions.