Mary L. Powelson

Potato Early Dying: Management Challenges in a Changing Production Environment

The potato (Solanum tuberosum L.) had its start in the Andean highlands of South America, where archeological evidence indicates it has been cultivated for at least 8,000 years (72). Today it is grown on all continents except Antarctica. Serving as a primary food source to indigenous people when the Spanish explorers arrived in Peru in the mid-1500s, the potato traveled the globe as a valuable staple, fueling armies, improving diets, and changing economies (Fig. 1). The importance of the potato goes beyond the feeding of nations, however. Today potato starch is used in the production of paper, adhesive, and textile goods, and in edible binding agents and low-fat food additives. The potato yields up a highly absorbent biodegradable material for use in disposable diapers. It provides starch products to keep oil well drilling bits smooth and to hold together the ingredients in lipsticks and cosmetic creams, and it provides a substance that works as a flocculation agent in water purification systems, replacing petroleumbased chemicals (33). China is the world’s largest producer of potatoes, followed by the Russian Federation (33). It is the most important vegetable crop in North America, where in 2000, nearly 690,000 ha were grown, with an average yield of 32.6 metric tons/ha and a farm gate value of over

Nutritional interactions influencing diseases of potato

2.7 billion. The potato is subject to several diseases caused by root-infecting pathogens. Two of particular significance are the soilborne fungi Verticillium dahliae and V. alboatrum. The potato root is also a host to the root-lesion nematode Pratylenchus penetrans. The two fungal pathogens alone, or in conjunction with P. penetrans, cause a disease called potato early dying (PED), also known as early die, early maturity wilt, and Verticillium wilt (64). This disease is endemic in many potato production areas of the United States, particularly in the Midwest and Pacific Northwest. In fields with a long history of potato production, it is a consistent yield constraint that requires intensive management. On land new to potato production, it may be absent in the first few years the crop is grown, but it almost invariably develops over time, requiring implementation of control measures to maintain high yields. In the last decade, the North American potato industry has undergone considerable changes. Production is increasingly being

Foliar fungicides as protective seed piece treatments for management of late blight of potatoes.

Nutrient management can decrease the severity of a number of important potato diseases, and certain practices, such as maintaining a low pH for scab control, have been followed for that single objective. More commonly, growers have incorporated fertility modifications into their particular disease and farming situations. Unfortunately, disease minimization may or may not be consistent with optimal fertilization for yield, quality, and profitability. Optimization for one disease may not match that for another, and the exact mechanisms involved are often complex and poorly understood. Potato growers will continue to experience conflicting production constraints. These constraints include price-driven needs for yield improvement and expense reduction; customer-driven demands for quality improvement; varietal shifts driven by the above considerations rather than by disease reduction; increasing pressure to justify, shift and reduce pesticide use; continuing concerns about nitrogen and phosphorus movement in groundwater and runoff; and increased attention to management of rotation crops.On the positive side, nutrient management strategies for highly specific situations continue to improve and practices addressing nutrient and disease variability within fields are becoming more sophisticated. In this context, there are opportunities for cultural management practices that reduce disease pressure and reliance on chemical controls. To be effectively integrated into such specialized management systems, the mechanisms of these control measures and the conditions under which they are practical will need to be better understood. Likewise, disease responses to these tactics need to be better quantified to allow an adequate cost-benefit analysis. With mounting concerns about the effects of agricultural pesticides on food safety, farm workers, and the environment, management of plant-available nutrients may become practical approaches for disease suppression in the future.ResumenEl manejo de nutrientes puede disminuir la severidad de muchas enfermedades importantes de papa y ciertas prácticas, tal como el mantener un pH bajo para el control de la sarna, se ha seguido con este simple objectivo. Con frecuencia, los productores de papa han incorporado modificaciones de la fertilidad con respecto a ciertas enfermedades en particular y condiciones de cultivo. Desgraciadamente, la reducción de la enfermedad puede ser consistente con una fertilización óptima para rendimiento, calidad y rentabilidad. Lo que puede controlar una enfermedad puede no ser bueno para otra enfermedad y los mecanismos involucrados son a menudo complejos e insuficientemente comprendidos. Los productores de papa continuarán experimentando limitaciones conflictivas en la producción. Estas limitaciones incluyen la influencia del precio de los artículos para mejorar el rendimiento y la reducción de los gastos; influencia de las demandas del consumidor para el mejoramiento de la calidad; cambios de variedad debido a las consideraciones anteriores más que a la reducción por enfermedades; incremento en la presión para la justificación; cambios y reducción en el uso de pesticidas; preocupación continua acerca del movimiento del nitrógeno y fósforo en el agua del suelo y su pérdida y un aumento de atención en la rotación de cultivos. En el lado positivo, las estrategias en el manejo de nutrientes para situaciones altamente específicas continúan mejorando y las prácticas referentes a los nutrientes y la variabilidad de las enfermedades dentro del campo se están volviendo más sofisticadas. En este contexto, existen oportunidades para el manejo de practicas culturales que reducen la presión de la enfermedad y la confianza en el control químico. Para estar efectivamente integrado a tales sistemas especializados de manejo, el mecanismo de estas medidas de control y las condiciones bajo las cuales son practica, necesitarán ser mejor comprendidas. Asimismo, las respuestas de estas tácticas necesitan ser mejor cuantificadas para permitir un adecuado análisis costo-beneficio. Con referencia a los efectos de los pesticidas agrícolas en la seguridad alimentaria, los trabajadores y el medio ambiente, el manejo de los nutrientes disponibles para la planta pueden convertirse en una manera de enfocar la practica para la supresión de enfermedades en el futuro.

Effect of Registered Potato Seed Piece Fungicides on Tuber-borne Phytophthora infestans

Fungicides receiving Section 18 emergency exemptions for management of the foliar phase of late blight of potato were evaluated as protective treatments for control of tuberborne inoculum of Phytophthora infestans in greenhouse and field studies. Three Section 18 products, Acrobat MZ (dimethomorph + mancozeb), Curzate M-8 (cymoxanil + mancozeb), and Tattoo C (propamocarb hydrochloride + chlorothalonil), when applied to the seed piece prior to inoculation with P. infestans, significantly (P ≤ 0.05) increased sprout emergence, compared with the inoculated water control. Of the three Section 18 products, Curzate M-8 was frequently the most effective. The increase in plant emergence with the protective seed piece treatment was seen with cultivars that differ in susceptibility to late blight, two genotypes (US-8 and US-11) of P. infestans, zoospore and sporangial inocula, and at different inoculation sites on the seed piece. In greenhouse studies, percent emergence with the protective seed piece treatments averaged 74% for cv. White Rose and 44% for cv. Shepody, compared with 9 and 8% for the inoculated water control of the respective cultivars. In field studies, when inoculum was placed either adjacent to or 4 cm away from the sprout, plant emergence of the inoculated water control was 12 and 36%, respectively. Application of the fungicides to the seed piece prior to inoculation increased emergence by an average of 700 and 212% for the respective inoculation sites. There was no evidence for translocation of the fungicides to the emerging foliage in concentrations high enough to prevent foliar infection from airborne inoculum of P. infestans. Control of tuberborne inoculum of P. infestans with appropriate seed piece treatments will result in an increase in plant emergence and improved crop uniformity.

Late blight resistant potato germplasm release AWN86514-2

Curative applications of thiophanate-methyl + mancozeb to blighted seed pieces of three potato (Solanum tuberosum) cultivars significantly reduced the amount of surface area colonized by Phytophthora infestans compared with treatment with thiophanate-methyl or no fungicide under laboratory conditions. Percent blighted tuber surface area over six tests averaged 3.5, 11.4, and 21.2% for the three treatments, respectively. Seed pieces inoculated with P. infestans US-8 or US-11 incubated, and then treated with the same fungicides and planted at Oregon and Washington field sites, respectively, had higher emergence across locations for thiophanate-methyl + mancozeb than for thiophanate-methyl (30 versus 12.5%). Emergence of healthy thiophanate-methyl + mancozeb-treated seed pieces averaged 93%. When protective applications of these fungicides, mancozeb, or fludioxinil were made to healthy potato seed pieces prior to inoculation with P. infestans, plant emergence in the greenhouse was significantly increased with thiophanate-methyl + mancozeb compared with fludioxinil (92 versus 36%) in Oregon and with thiophanate-methyl or fludioxinil (90 versus 20 and 24%) in Washington. Inoculation of healthy seed pieces reduced plant stand in all greenhouse tests; however, treatment with thiophanate-methyl + mancozeb or mancozeb alone prior to inoculation resulted in sprout emergence similar to that of the noninoculated control. In a late blight management program, treatment of seed pieces with a registered fungicide that has activity against P. infestans contributes to an increase in plant emergence and improved crop uniformity. However, for maximum benefit, the fungicide must be in place before coming in contact with the pathogen.

Seasonal incidence and cause of blackleg and a stem soft rot of potatoes in Oregon.

Potato breeding selection AWN86514-2, Solanum tuberosum gp tuberosum, is being released as germplasm that is highly resistant to prevalent North American strains of Phytophthora infestans. This selection has been tested under field conditions in Mount Vernon, Washington (P. infestans US11 and US8 with complex virulence pathotypes), as well as Corvallis, Oregon, and eight other locations in North America (predominantly P. infestans US8) between 1994 and 1997. Both foliage and tubers show partial resistance. Although AWN86514-2 is pollen sterile, it can be successfully used as a female parent. An average of 34% of the progeny from crosses between AWN86514-2 and four susceptible clones were resistant to late blight when tested at Toluca, Mexico, in 1996. AWN86514-2 also has high resistance to Verticillium wilt and potato virus Y. AWN86514-2 is late maturing, with medium yields of smooth, longoblong, buffskinned tubers. Specific gravity is high and french fry color from 7 C (45 F) storage is excellent. The male parent of AWN86514-2 was Ranger Russet, a dual purpose french fry and fresh market variety, and the female parent was KSA195-96, a selection made at Aberdeen, Idaho, from Polish germplasm received as true seed from the Polish Plant Breeding and Acclimatization Institute. Possible sources of the late blight resistance in this clone include S. acaule, S. demissum, S. phureja, S. simiplicifolium, S. stoloniferum, and S. tuberosum gp andigena which are in the lineage of KSA195-96. This germplasm was developed and released by USDA-ARS in cooperation with the Agricultural Experiment Stations of Idaho, Oregon, and Washington.

Potato early dying disease in the Pacific Northwest caused byErwinia carotovora pv.carotovora andE. carotovora pv.atroseptica

Blackleg of potatoes in a center pivot irrigated circle of Kennebec potatoes in Oregon’s Columbia Basin was caused by eitherErwinia carotovora var.atroseptica (Eca) orE. carotovora var.carotovora (Ecc). Eca was recovered only early in the growing season whereasEcc was associated with blackleg symptoms later in the season.A soft rot, atypical of blackleg, was widespread throughout the circle and was most prevalent during the latter part of the growing season. Initially, the vines near the soil surface appeared translucent and watery and were soft and mushy to the touch. The pathogen associated with this symptom was exclusivelyEcc.ResumenLa pierna negra de la papa en un círculo de papa Kennebec con riego de pivote central en la Cuenca del Río Columbia en el Estado de Oregon fue causada tanto porErwinia carotovora var.atroseptica (Eca) como porE. carotovora var.carotovora (Ecc). Sólo se obtuvo Eca al comienzo del período vegetativo, mientras que Ecc estuvo asociado con pierna negra mas tarde en la temporada.Una podredumbre blanda, atípica de pierna negra, estuvo ampliamente diseminada a través del círculo y fue mas prevalente durante la segunda mitad del período vegetativo. Al comienzo, los tallos cerca de la superficie del suelo tomaron una apariencia traslúcida y acuosa y eran suaves y mucilaginosos al tacto. El patógeno asociado exclusivamente con este síntoma fue Ecc.

Association of viral, bacterial and fungal pathogens with vascular discoloration of Russet Burbank potato tubers

Premature death of potato vines is widespread in irrigated potato fields of the Pacific Northwest.Verticillium dahliae is a major cause of early dying in fields with a history of potato production, but in fields new to potato production, or those that have been fumigated and have a lowV. dahliae population in the soil, premature death of vines can also occur.Erwinia carotovora pv.carotovora (Ecc) andE. carotovora pv.atroseptica (Eca) have been implicated in the early dying disease syndrome in these fields. Both bacterial pathogens are associated with symptoms similar to those caused byV. dahliae; i.e., a progressive chlorosis and necrosis of the foliage and vascular discoloration that may extend a short distance up the stem. Greenhouse pathogenicity studies on cv. Russet Burbank cuttings in which symptom development was identical to that produced byV. dahliae have verified thatEcc andEca can cause potato early dying.ResumenLa muerte prematura del rastrojo de la papa (MPP) es común en suelos irrigados del Pacifico noroccidental.Verticillium dahliae es la causa principal de la MPP en campos con historial de producción de papa, pero la MPP también puede ocurrir en campos nuevos para este cultivo, o en aquéllos qu han sido fumigados y tienen una población baja deV. dahliae en el suelo.Erwinia carotovora pv.carotovora (Ecc) yE. carotovora pv.atroseptica (Eca) nan sido relacionados con la MPP en éstos últimos campos. Ambos patógenos bacterianos están asociados con sintomas similares a los causados porV. dahliae, tales como clorosis progresiva y necrosis del follaje y descoloración vascular que se puede extender un poco por el tallo mismo. En estudios de invernadero con esquejes del cultivar Russet Burbank, se observó que el desarrollo de los síntomas fue idéntico al producido porV. dahliae con lo cual se ha verificado que Ecc y Eca pueden causar la muerte prematura de la papa.

THE AMERICAN PHYTOPATHOLOGICAL SOCIETY

Russet Burbank potatoes from the 1979 and 1980 crop years, collected from Chicago, IL repack warehouses and retail markets, were sampled for vascular discoloration. The amount of discoloration varied among sampling months and states of origin and decreased from 7.7% in 1979 to 1.6% in 1980. Highest levels of vascular discoloration were detected in December and January samples.Vascular discolored and non-discolored (control) tubers were assayed for the presence of potato leafroll, potato virus X, and beet western yellows viruses by the enzyme-linked immunosorbent assay (ELISA). Tubers were also assayed for 2 subspecies ofErwinia carotovora and forVerticillium albo-atrum andV. dahliae. Potato leafroll virus was detected in 31 of 831 vascular discolored tubers.V. albo-atrum was detected in 1 of 180 discolored tubers. Beet western yellows virus was not detected in discolored or non-discolored tubers. Two subspecies ofE. carotovora and potato virus X were equally common in discolored and non-discolored tubers.ResumenEn centrales de embalaje y en mercados minoristas de Chicago, Illinois, se recogieron muestras de papa, de las cosechas de 1979 y 1980 de la variedad de Russet Burbank, para pruebas de descoloración vascular. El grado de descoloración varió con los meses de muestreo y los lugares de origen, se redujo de 7.7% en 1979 a 1.6% en 1980. Los niveles más altos de descoloración vascular fueron detectados de las muestras de diciembre y de enero.Mediante ELISA fueron examinados tubérculos con descoloración vascular y sin descoloración (tubérculos testigos), para verificar la presencia de virus del enrollamiento de las hojas de la papa PLRV, de virus X de la papa y de virus del amarillamiento occidental de la remolacha (“beet western yellows”). También fueron sometidas a prueba dos subespecies deErwinia carotovora yVerticillium albo-atrum yV. dahliae. Se detectó el virus del enrollamiento de las hojas en 31 de 831 tubérculos con descoloración vascular. En 1 de 180 tubérculos descolorados se detectóV. albo-atrum. No se detectó virus de amarillamiento dental de la remolacha (“beet western yellows”) en tubérculos con descoloración o sin descoloracion. Fue frecuente la presencia de dos subespecies deE. carotovora y del virus X de la papa tanto en tubérculos descolorados como en los sin descoloración