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Abstract: A densely compacted soil layer has been a prevalent feature of the vegetable crop production region of Central Wisconsin, resulting in poor water drainage, increased susceptibility to tuber disease, and reduced yield and quality in potatoes. Subsoil tillage has been implemented on a wide-scale for management of problems associated with compacted soil layers. Pink eye is a tuber disorder that causes storage and processing losses. Periods of moisture stress and increased hill temperatures have been linked to pink eye incidence, but the cause of this disorder is unknown and few specific management recommendations exist. The goals of this work were to quantify the impact of compacted soils and subsoil tillage on development of potato pink eye. Small plot experiments were conducted to quantify response of soil conditions and potato pink eye to soil compaction and subsoil tillage. Compacted soils resulted in higher volumetric soil water content and extended periods of free water, especially after substantial precipitation events. Subsoil tillage allowed for more rapid movement of water following large precipitation events decreasing periods of free water. More compacted soils also had higher soil temperatures. Subsoil tillage delayed the development and progression of pink eye symptoms, but did not influence overall incidence. Increased soil moisture and temperature corresponded with more rapid development of pink eye in compacted and conventionally tilled soils. This research suggests subsoil tillage may be useful in reducing the severity of pink eye symptoms by alleviating compacted subsoil layers that limit water drainage. In addition, prevention of compaction reduced soil temperatures which limited pink eye development.

Potato virus Y(PVY) causes one of the most serious and widespread diseases in North America. In recent years, the virus has become increasingly difficult to control. Durable dominant genes for resistance to PVY exist in potato germplasm and provide an effective control strategy. This paper describes a Solanum chacoenseclone (M19) that is homozygous for a PVY resistance gene. The gene is linked to a previously published marker for Rychcfound in Solanum chacoense. M19 was crossed with a diploid S. tuberosumclone to produce an adapted clone carrying the resistance gene. This hybrid clone is named M20. M20 tuberizes in the field, producing round tubers with white skin and flesh and moderate size. M20 is resistant to PVYO, PVYN:O, and PVYNTN. Both M19 and M20 are female and male fertile, so they are being released as sources of PVY resistance for breeding programs. El Virus Y de la Papa(PVY) causa una de las enfermedades más serias y de amplia distribución en Norteamérica. En años recientes, el virus ha aumentado la dificultad para su control. Los genes durables dominantes para resistencia al PVY existen en el germoplasma de papa y proporcionan una estrategia de control efectivo. Este artículo describe un clon (M19) de Solanum chacoenseque es homozigótico para un gen de resistencia al PVY. El gen esta ligado a un marcador previamente publicado para Rychcencontrado en Solanum chacoense. Se cruzó M19 con un clon diploide de S. tuberosumpara producir un clon adaptado llevando el gen de resistencia. A este clon híbrido se le llama M20. Este clon tuberiza en el campo, produciendo tubérculos redondos con piel y pulpa blancas, de tamaño moderado. M20 es resistente al PVYO, PVYN:Oy PVYNTN. Ambos M19 y M20 son fértiles como hembra y macho, de manera que están siendo liberados como fuentes de Resistencia al PVY para los programas de mejoramiento.

Potato virus Y(PVY) is the most important virus in North American seed potato (Solanum tuberosumL.) production. Planting virus-free minitubers in place of field-grown seed, which usually has a low PVY incidence, reduces initial PVY inoculum in the field. However, plants grown from minitubers are smaller and emerge later than those grown from conventional seed, which could make them more likely to become infected with PVY. We tested the effects of seed type of three potato cultivars (Dark Red Norland, Goldrush, and Red La Soda) on PVY incidence, tuber yield, and flowering time. The incidence of PVY in plants grown from minitubers did not differ from that of plants grown from conventional seed. Minituber-grown plants produced lower tuber yields than plants grown from conventional seed. Plants from minitubers also emerged and flowered later, but this did not increase their incidence of PVY. Cultivar-specific differences were observed in tuber yield and flowering times, suggesting that this variation may influence PVY incidence more than seed type. El virus Y de la papa (PVY) es el más importante en la producción de semilla de papa (Solanum tuberosumL.) en Norteamérica. La siembra de minitubérculos libres de virus en lugar de la semilla obtenida del campo, que generalmente tiene una baja incidencia de PVY, reduce el inóculo inicial de PVY en el campo. No obstante, las plantas a partir de minitubérculos son más pequeñas y emergen más tarde que aquellas cultivadas de semilla convencional, que las pudiera hacer más propensas a infectarse con PVY. Nosotros probamos los efectos del tipo de semilla de tres variedades de papa (Dark Red Norland, Goldrush, y Red La Soda) sobre la incidencia de PVY, rendimiento de tubérculo y tiempo de floración. La incidencia de PVY en las plantas cultivadas a partir de minitubérculos no difirió de las cultivadas de semilla convencional. Las plantas de minitubérculos produjeron rendimientos de tubérculo más bajos que las de semilla convencional. Las plantas de minitubérculos también emergieron y florecieron más tarde, pero esto no aumentó su incidencia de PVY. Las diferencias específicas por variedad se observaron en rendimiento de tubérculo y tiempos de floración, lo que sugiere que esta variación pudiera influenciar la incidencia de PVY más que el tipo de semilla.

AbstractA new leaf spot disease was observed on leaves of Rheum palmatum(Chinese rhubarb) in Northwest China (Gansu Province) starting in 2005. A Septoria-like fungus was isolated and completion of Koch’s postulates confirmed that the fungus was the casual agent of the leaf spot disease. Morphology and molecular methods were combined to identify the pathogen. The fungus produced conidiomata pycnidia and the conidia were 2~5 septate, 61.2~134.1 μm in length and 3.53~5.3 μm in width, which is much larger than the known Spetoriaspecies that infects Polygonaceae species. Phylogenic analysis of the internal transcribed spacer region confirmed that this Septoria-like fungus is within the Septoriagenus but distinct from known Septoriaspecies. Together, these morphological and phylogenetic data support that the R. palmatuminfecting Septoriastrain is a newlydescribed plant pathogenic species.

Potato virus Y(PVY) is responsible for the majority of seed potato lot rejections in North America. Some commercial cultivars and breeding lines have major genes for PVY resistance, but their use in North American breeding programs has been limited. Marker assisted selection of PVY resistance can increase the efficiency of identifying resistant plants and integrating resistance into new cultivars. We used markers RYSC3 and YES3-3B, linked to genes Ryadgand Rysto, respectively, to screen 46 breeding clones and cultivars, and identified 19 resistant clones. Resistant parents were crossed with susceptible parents with good market and agronomic traits and molecular marker analysis of each family showed a 1:1 segregation ratio. The persistence of this segregation ratio over 2 years of selection and the lack of major linkage drag as assessed by a breeder rating indicated that there was no evidence of an association of PVY resistance with undesirable traits. El virus Y de la papa (PVY) es responsable por la mayoría de los rechazos de los lotes de papa para semilla en Norteamérica. Algunas variedades comerciales y líneas de mejoramiento tienen genes mayores para resistencia al PVY, pero es limitado su uso en programas de mejoramiento de Norteamérica. La selección asistida con marcadores de resistencia al PVY puede aumentar la eficiencia en la identificación de plantas resistentes y en la integración de la resistencia a nuevas variedades. Nosotros usamos los marcadores RYSC3 y YES3-3B, ligados a los genes Ryadg y Rysto, respectivamente, para evaluar 46 clones y variedades, e identificamos 19 clones resistentes. Se cruzaron padres resistentes con susceptibles de buenas características agronómicas y de mercado, y el análisis de marcadores moleculares de cada familia mostró una relación de segregación de 1:1. La persistencia de esta relación de segregación en dos años de selección, y la carencia de ligamiento mayor de arrastre evaluada por calificación de un fitomejorador, indicaron que no hubo evidencia de una asociación de la resistencia del PVY con caracteres no deseables.