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Understanding the Recent Outbreak of Dickeya dianthicola Causing Potato Soft Rot and Blackleg in the United States
Jianjun Hao: University of Maine; Amy Charkowski: Colorado State University; Steve Johnson: Univ of Maine Coop Ext; Gary Secor: North Dakota State University
<div>An outbreak of <i>Dickeya</i> caused disease occurred in 2015 and 2016 in the Eastern US, and <i>D. dianthicola</i> has been determined to be the major causal agent. This problem continues to be a threat since then and <i>D. dianthicola</i> has been found in at least 23 states in the US. Furthermore, multiple <i>Pectobacterium</i> spp. are frequently found in blackleg and soft rot samples along with <i>D. dianthicola</i>. This pathogen complex causes significant economic losses throughout the season due to low emergence and necrotic stems during the growing season and rotted tubers in storage. Contaminated seed potato tubers are a major source of inoculum, but the bacteria can survive and spread on crops other than potatoes, and can survive in the environment, particularly in surface water. Pathogen detection by PCR from tuber stem ends or periderm is a primary tool to evaluate seed potato lots for Dickeya and test results are used to eliminate seed lots with high pathogen incidence from production. Unfortunately, most published detection primers failed when we attempted to validate them with field samples. Sanitation and proper handling of tubers at planting and storage can reduce disease spread. Five antibacterial products were tested to identify additional chemicals farmers could use for sanitation. Elite breeding lines were screened to identify resistant or tolerant lines. To better understand the outbreak, researchers are focused on strain identification, the effect of climate, as well as pathogen distribution, spread and biology. Findings such as where <i>D. dianthicola</i> resides on potato tubers and how it goes to dormant state will improve the efficiency of detection and elimination of pathogens.</div>

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