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POSTERS: Population biology and genetics

Sweet corn production in the Columbia Basin of Washington: Causal agents of seedling blights and prevalence of mefenoxam resistance
Ryan Solemslie - Washington State University. Michael Derie- Washington State University, Paul Morgan- Washington State University, Lindsey du Toit- Washington State University, Sanjaya Gyawali- Washington State University

Washington State is a major producer of sweet corn in the USA with roughly 36,400 ha planted in the semi-arid Columbia Basin annually. However, cold spring soil conditions and pathogenic species of Fusarium, Pythium, and Rhizoctonia can cause significant yield losses. In 2018, conventional (n = 32) and organic (n = 16) sweet corn fields were surveyed in the Columbia Basin to assess the prevalence of damping-off and seedling blights. Isolations from stunted seedlings primarily yielded Fusarium, Pythium, and Rhizoctonia. Pythium ultimum comprised 95.2% of 63 Pythium isolates based on sequencing the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA), with only one isolate of each of P. irregulare, P. rostratifingens, and P. sulcatum. Of 66 Rhizoctonia isolates, 69.7% were R. solani AG-4 based on ITS rDNA sequences. Of 370 Fusarium isolates identified by sequencing the translation elongation factor 1-alpha gene, F. equiseti, F. oxysporum, F. solani, and F. verticillioides were most prevalent. Of the 63 collected Pythium isolates, 62 Pythium isolates screened for mefenoxam resistance, 38 and 35 were resistant to mefenoxam at 10 and 100 ppm, respectively. The high incidence of mefenoxam resistance may account for some stand losses in fields planted with mefenoxam-treated seed. Isolates from each genus are being tested for pathogenicity to sweet corn, and the most virulent isolates used to screen sweet corn germplasm for resistance to seedling blights.