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An overview of challenges and changes in potato production and potato diseases in the United States and Canada

Amy Charkowski: Colorado State University

<div>The only known major pathogens that caused bacterial blackleg and soft rot of potato in North America used to be <em>Pectobacterium atrosepticum </em>and <em>P. carotovorum</em>. However, even early genomics methods demonstrated that multiple previously undescribed <em>Pectobacterium</em> species caused blackleg and soft rot. Available phylogenetic and genomic data suggests that additional species remain to be described in the United States. Over the past decade, multiple species capable of causing these diseases were identified and sequenced. In 2014, a blackleg outbreak caused by <em>D. dianthicola</em> was identified and this pathogen quickly spread to multiple potato-producing regions via seed potatoes. Two distinct<em> D. dianthicola</em> strains were identified in multiple states during outbreak, but other <em>Dickeya</em> species do not appear to play a major role in blackleg in North America. <em>D. dianthicola</em> was often found with <em>Pectobacterium</em>, with <em>P. parmentieri </em>appearing to be one of the most common co-occurring species. Changes in potato varieties and testing of new potato varieties may have contributed to the recent <em>D. dianthicola</em> outbreak. Improvements in seed lot testing, including a new PCR assays developed from genomic analyses have reduced blackleg incidence over the past two growing seasons. Seed potato certification data has provided some information on potato lines that tolerate blackleg or that are highly susceptible. Further screening material for resistance is difficult due to the high variability in disease tolerance caused by plant age and environment, so virulence assays that provide improved quantitative ratings of disease tolerance were developed.</div>

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