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Fungicide sensitivity of Rhizoctonia spp. isolated from soybean fields in Nebraska

Nikita Gambhir: University of Nebraska

<div>Soybean seedling diseases reduce stand establishment and cause economic losses. <em>Rhizoctonia </em>species are important causal agents in Nebraska. For effective disease control, the prevalent <em>Rhizoctonia spp.</em> need to be characterized. Soil and symptomatic plants were collected from a total of 54 soybean fields in Nebraska in 2015, 2016, and 2017. Soil samples were collected in a ‘W’ or ‘Z’ pattern from a depth of 0-6”. Sugarbeet and toothpick bait methods were used to isolate <em>Rhizoctonia spp</em>. from soil. A total of 48 <em>Rhizoctonia spp.</em> were isolated. ITS sequencing was used to determine species and AG. The most abundant were <em>R. zeae </em>(26) and <em>R. solani</em> AG 4 HG-II (14). Fungicide seed treatments are commonly used to manage soybean seedling disease and include several modes of action, such as SDHI, QoI, and Phenylpyrroles. Few studies have examined fungicide sensitivity of <em>Rhizoctonia </em>from soybean fields and none have characterized sensitivity of populations in Nebraska. Current work is underway to determine fungicide sensitivity of isolates obtained in the present study. Fungicide sensitivity of isolates will be determined using a plate dilution method for three fungicides: Fluxapyroxad (SDHI), Azoxystrobin (QoI), and Fludioxonil (Phenylpyrroles). Effective concentration for 50% inhibition (EC<sub>50</sub>) will be estimated from a dose-response curve. Results will establish sensitivity of <em>Rhizoctonia spp </em>in Nebraska and can be used for monitoring sensitivity shifts in future.</div>