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Isolation and Identification of Bacteria Causing Blackleg and Soft Rot of Potato in Northeastern U.S.

Tongling Ge: University of Maine

<div>Both <em>Dickeya</em> and <em>Pectobacterium</em> spp. are important causal agents of blackleg and soft rot of potato and result in significant economic losses. Since 2015, when an outbreak occurred, blackleg has been a problem in the Northeastern U.S. Samples from symptomatic plants, dormant tubers, and surface irrigation water were collected in 2015, 2016 and 2017 to study this disease. These samples were mainly from Maine, with small portion also from other Eastern states where Maine seed tubers were planted. <em>Dickeya</em> and <em>Pectobacterium</em> spp. were isolated and purified from the samples on selective medium crystal violet pectate agar. Genomic DNA of the bacteria was extracted and amplified in polymerase chain reactions using <em>Dickeya</em> and <em>Pectobacterium</em> genus-specific primers to confirm their taxonomy. Furthermore, the <em>gapA</em> gene of the isolates was amplified and the amplicons were sequenced and blasted against the GenBank database to identify bacteria to species. <em>Dickeya dianthicola,</em> <em>P. parmentieri</em>, and <em>P. carotovorum </em>were identified from potato plant and tuber isolates. Nearly 43% of water samples were either <em>Dickeya</em> or <em>Pectobacterium</em> positive; <em>Dickeya zeae, D. dianthicola,</em> <em>D. dadantii, P. parmentieri</em>, and <em>P. carotovorum </em>were found in water samples. Isolates will be used in genetic diversity analysis of <em>Dickeya</em> and <em>Pectobacterium</em> spp. on potato. Further investigation will help to understand the epidemiology and impact of irrigation water on the disease.</div>