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2017 APS Annual Meeting PhytoView

Engage in facilitated conversations that explore questions/issues of regulatory, policy, research, extension, and education in plant pathology as we explore all points of view.


Seedborne vs. Seed Transmitted Plant Pathogens:
The Curious Case of Phomopsis spp. on Spinach Seed

 2:45—4:00 p.m.

Organizer: Ron Walcott, The University of Georgia, Athens, GA

To most, the terms seed-borne and seed transmitted are indistinguishable and often are used interchangeably.  However, these terms have distinct implications for seed producers, growers, and regulatory agencies.  For example, the term seed-borne represents microorganisms (plant pathogens and non-plant pathogens) that may be present in or on seeds.  In contrast, seed transmitted suggests that seed-borne organisms are likely to be transmitted to germinating seedlings/plants and, if the organisms are plant pathogens, initiate plant disease outbreaks.  Hence, seed producers and governmental regulatory agencies should be more concerned with seed-borne plant pathogens for which there is a high risk of seed transmission in the environments in which the seed will be planted.  This risk must be determined empirically to avoid unnecessary costly and burdensome regulations, while facilitating the safe movement of seeds across geopolitical borders.  Hence, assuming (incorrectly) that all seed-borne organisms are seed transmitted could have negative impacts on seed trade.  Interestingly, some seedborne microorganisms may not be a threat to the carrier seed species, but may present a threat to other plant species. Such is the case of Phomopsis spp. on spinach seeds. This curious case raises a conundrum that challenges norms and has created disarray from a regulatory and seed trade perspective. This Phytoviews session will explore the nuanced differences between seed-borne and seed transmitted pathogens, including the implications of these terms for researchers, seed producers, growers, and regulatory agencies.  Three panelists will share the connotations of seed-borne vs. seed transmitted from the perspectives of a university seed pathologist, a commercial seed producer, and a regulatory agency.  Finally, Phomopsis spp. detected on spinach seed will be used to highlight a unique challenge presented by seedborne organisms that might not be seed transmitted, and for which the taxonomic state of flux of this genus has prevented the development of a resolution to a seed trade quarantine.


  • Lindsey DuToit, WSU Mount Vernon Northwestern Washington Research & Extension Center (NWREC), Mount Vernon, WA
  • Ric Dunkle, American Seed Trade Association, Alexandria, VA
  • Christina Devorshak, USDA/APHIS – PPQ, CPHST, Raleigh, NC