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POSTERS: Population biology and genetics

Molecular identification and comparison of Sclerotium cepivorum isolates causing Allium white rot in Nevada
Shouhua Wang - Nevada Dept of Agric. Megan Li- Davidson Academy of Nevada, Jade Wang- Davidson Academy of Nevada, Jennifer Schoener- Nevada Department of Agriculture

White rot caused by Sclerotium cepivorum has been the biggest threat to Allium crop production in Nevada. Over the years, infections of white rot have been found in Washoe, Douglas and Lyon counties. Diagnosis of Allium white rot is generally based on symptoms and microscopic examination of fungal mycelium and sclerotia, and the molecular identity of the pathogen and its potential variants among those isolates have not been investigated. In this study, we used rDNA and ITS regions to compare 7 isolates collected from 3 counties during 2014-2017. An individual sclerotium was placed onto potato dextrose agar and incubated at 22?C in the dark. Genomic DNA was extracted from single sclerotium isolates (SSIs), regions of rDNA were amplified using ITS1/4 primers, and PCR products were subcloned into pGEM®-T vector and sequenced. A consensus DNA sequence of a 540-bp PCR fragment was obtained for each isolate by aligning multiple cloned sequences. Alignment analysis revealed that 5 out of 7 SSIs had the same amplicon sequence (Accession No. MK577439) that is 100% identical to the corresponding regions of S. cepivorum voucher NKI 286 (Accession No. FJ460433). Two SSIs had only one nucleotide substitution. Our data confirmed that these 7 isolates were S. cepivorum and there were no significant variations in the rDNA or ITS regions. Lack of molecular variation among these isolates suggests that white rot infections in Nevada may have originated from a common source.