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Emerging understanding of the pathogenesis of Rhizoctonia zeae in row crops

Srikanth Kodati: University of Nebraska Lincoln

<div><em>Rhizoctonia zeae</em> is a multinucleate <em>Rhizoctonia</em>, reported as a major soil borne pathogen in turf but not well reported in row crops. While a literature search showed a brief report of <em>R. zeae</em> on corn, there is none for soybean or wheat. In a statewide survey of <em>Rhizoctonia</em> spp. in row crops in Nebraska from 2016-2017, a surprisingly large number of <em>R. zeae</em> isolates were recovered. The objective of this study was to determine the taxonomic diversity of the recovered <em>R. zeae</em> isolates and examine their pathogenicity on corn, soybean, and wheat. A total of 71 <em>R. zeae</em> isolates (34 in 2016 and 37 in 2017) were recovered from 17 fields in 9 counties of the state in 2016 and 2017. Isolates were identified through morphology and sequencing with internal transcribed spacer (ITS) 4 and 5 primers. Pathogenicity tests were conducted by inoculating all isolates onto soybean through a repeated rolled towel assay and greenhouse assay methods. Visual rating of symptoms on the root and crown was done to determine disease severity. Strains that were virulent on soybean were also screened for pathogenicity on wheat and corn. Among a total of 71 <em>R. zeae</em> isolates collected, 60 (84.5%) were pathogenic on soybean. Among them, eleven strains showed high aggressiveness and virulence on all the three crops at levels that were not significantly different (p = 0.05) from the virulent <em>Rhizoctonia solani</em>. Multiple strategies are being explored to further understand pathogenesis in <em>R. zeae</em>.</div>