About the Author
Since beginning his career at North Dakota State University in 1974, Richard T. Zink has focused on potato pathology, seed production, and seed certification. He managed the seed potato certification program in Minnesota for eight years before moving to his current position as Extension Potato Specialist at Colorado State University in 1992. His ongoing research projects emphasize control of bacterial and fungal diseases as well as cultivar-specific management. He is past Chair of the Pathology and Certification Sections of the Potato Association of America and now works closely with the National Potato Council on international seed potato trade issues. Zink received his B.S. and M.S. in Plant Pathology from North Dakota State University and Ph.D. in Plant Pathology from Kansas State University.
Will Late Blight be Mitigated Through Regulation?
Richard T. Zink
Colorado State University
The application of laws and regulations to the management of plant disease is a well-established practice. One of the most successful examples of this has been the control of black stem rust of wheat through the barberry eradication law. The stem rust control program has worked because it is based on sound biology. There are numerous other examples of plant diseases that have been controlled through laws directed at either the host, the pathogen, or the conditions that foster disease. It is important to note that in each case success has been the result of a clear understanding of the disease and that regulatory measures were only utilized in concert with other disease management tools.
Historically, control of late blight of potato caused by Phytophthora infestans has not relied heavily on phytosanitary laws or regulations. Until recently, regulatory measures pertaining to late blight have resided primarily within seed potato certification protocols. Among certification programs most do not have a tolerance for late blight in the field unless the disease is so extensive that it interferes with the inspection process. Otherwise, the generally accepted tolerance for late blight has been one percent disease in seed tubers at the time of shipment. In addition to tolerances in seed, several areas in the U.S. have also maintained laws addressing cull potatoes and their disposal.
Regulatory interest in late blight began to change following the establishment of new highly aggressive genotypes of P. infestans in North America. For reasons that are not clear, the potential for seedborne dissemination of late blight increased dramatically. The long standing one percent tolerance for late blight in seed proved to be ineffective and the disease quickly appeared in almost every potato production area in North America. Out of frustration, individual potato growers and even whole industries began accusing each other of being the source of the problem. Within a short time there were discussions at the national, state, and local levels about the need for greater scrutiny of seed lots, imposing additional testing of seed specifically for late blight and greatly reducing the tolerance for late blight in seed. Several states quickly enacted laws that placed rigid restrictions on imported seed potatoes in an effort to avoid further introductions of late blight.
In general, laws that deal with cull potatoes and containment of disease outbreaks are biologically sound and have a historical record of effectiveness. Conversely, quarantines and regulations based primarily on a specific tolerance for late blight and visual detection of disease in seed are inherently flawed. Visual inspections for late blight have proven inadequate and there are no precise or rapid assays to directly detect P. infestans in tubers or seed shipments. Furthermore, there is no scientific evidence to support the theory that reducing the tolerance for late blight tuber decaying seed will reduce disease in the field. Simply lowering the tolerance for late blight in seed could create a false sense of security and in fact increase the risk for disease.
Biological and technical limitations notwithstanding, there remain several ethical and jurisdictional issues to be addressed. For example, is it appropriate for all seed from one region of the country to be discounted just because a few growers may have had late blight? Does the federal government have a role in late blight regulatory affairs, or should authority reside at the state level or within seed potato certification agencies? Should one organization such as The National Potato Council have the lead role in setting regulatory policy? Is it rational to elevate P. infestans to quarantine status among states or between trading countries? And lastly, what will be the real costs of any far-reaching late blight regulation if it polarizes the industry?
At some point regulatory measures may play an important role in mitigating the impact of late blight on North America's potato industry. It is imperative, however, that such regulations be based on science and not driven by emotion.
TIZON TARDIO PODRIA SER MITIGADO A TRAVES DE REGULACIONES
Richard T. Zink
La aplicacion de leyes y regulaciones al manejo de enfermedades de plantas es una practica muy bien establecida. Uno de los ejemplos de mayor exito ha sido el control de roya del tallo del trigo a traves de la erradicccion de berberry por mandato de ley. El programa de control de la roya del tallo ha trabajado porque esta basado en un proceso biologico. Hay muchos ejemplos de emfermedades de plantas que han sido controlados a traves de leyes directas tanto del patogeno como del huesped o de condiciones foster de la enfermedad. Es importante recalcar que en cada caso, los logros han sido el resultado de un entedimiento claro de la enfermedads y de procesos regulatorios que solamente fueron utilizados en acuerdo de otros instrumentos de manejo de enfermedades.
Historicamente, control de tizon tardio de la papa causado por Phytopthora infestans no ha sido logrado en terminos confiables a traves de leyes o regulaciones fitosanitarias. Hasta hace poco, medidas regulatorias pertinente a tizon tardio ha residido primeramente dentro de registro de semilla de papa. Acerca de programas de certificacion, los mas no tienen tolerancia al tizon tardio a nivel de campo a menos que la enfermedad este muy extendido y que interfiera con los procesos de inpeccion. Por otra parte, la tolerancia aceptada para tizon tardio generalmente ha sido el 1 % en semilla de papa infectada al momento de su embarque. Ademas de la tolerancia en la semilla en muchas areas de los EEUU han sido fijadas tambien leyes dirigidos a escoger papas y su disposicion.
Intereses regulatorios de tizon tardio empeso despues de que el nuevo genotipo muy agresivo de P. infestans fue establecido en Norte America. Por razones que no son muy claros, potencialmente la diseminacion del tizon tardio por intermedio de la semilla se incremento dramaticamente. La permanencia por mucho tiempo del 1 % de tolerancia para tizon tardio en semilla probo ser inefectivo y la enfermedad aparecio rapidamente en todas las zonas produstoras de papa en Norte America. Despues de mucha fustracion, productores individuales y en casos toda la industria empezo acusandose cada uno de ser la fuente del problema. En un corto tiempo hubieron discusiones a nivel nacional, estatal y local acerca de la necesidad por un mejor escrutinio de los lotes de semilla de papa, imponiendo adicionales muestreos de semilla especificamente para tizon tardio y reduciendo enormente la tolerancia para tizon tardio en la semilla. Muchos estados rapidamente establecieron leyes que fijaban rigidas restricciones a la importacion de semilla de papa en un esfuerzo de evitar futuras introducciones de tizon tardio.
En general, leyes que tienen que tratar con la eleccion de papas y la represion de los resurgimientos de la enfermedad son buenos biologicamente y tienen un record de efectividad. Inversamente, cuarentenas, regulaciones basados primeramente en una tolerancia especifica para tizon tardio y detecciones visuales de la enfermedad en la semilla son inherentemente defectuosos. Inspeciones visusles para tizon tardio han probado ser inadecuados y no exite pruebas rapidas, precisas y directas para la deteccion de tizon tardio en tuberculos o semilla embarcadas. Consecuentemente, no hay una evidencia cientifica que soporta la teoria de que reduciendo la tolerancia a tizon tardio en los tuberculos deterirados como semilla va ha reducir la incidencia de infeccion a nivel de campo. Simplemente bajando el porcentaje de tolerancia a tizon tardio en la semilla podria crear un falso sentido de seguridad y en efecto incrementar los riesgos de la enfermedad.
Limitaciones biologicas y tecnicas no obtante, permanecen muchos principios de etica y juridiscionales de ser aplicados. Por ejemplo, es inapropiado para la semilla de toda una region de un pais de ser desestimado solamente por que pocos productores pueden tener tizon tardio. El govierno federal tiene reglas en el asunto de regulaciones del tizon tardio o deberia la autoridad residir a nivel estatal o dentro de las agencias de certificacion de semilla de papa. Deberia una organizacion como el de National Potato Council tener el liderazgo en el rol de sentar politicas regulatorias. Es racional elevar P. infestans a una categoria de cuarentena entre los estados o entre los paises con los que se comercia. Y finalmente, cual debera ser el costo real de cualquier regulacion del tizon tardio por mas lejos que llegue y si polariza la industria.
En algun punto las medidas regulatorias podrian jugar un rol importante en mitigar el impacto del tizon tardio en la industria de la papa. Esto es imperativo sin embargo, que estas regulaciones deben basarse en la ciencia y no dejarse llevar por las emociones.
