J. M. Crosslin

Effect of Hairy Nightshade (Solanum Sarrachoides) Presence on Potato Nematodes, Diseases, and Insect Pests

Abstract Hairy nightshade is a common weed in potato rotations in the western United States. As a close relative of potato, hairy nightshade can host numerous potato nematodes, diseases, and insect pests. Hairy nightshade hosts three common parasitic nematodes of potato, Columbia and northern root-knot nematodes, and stubby root nematode. Tubers of a potato breeding line with roots that are resistant to Columbia root-knot nematode—race 1, were damaged when grown in the presence of hairy nightshade. The weed provided an alternate host for the nematode, which then allowed the nematode to infect susceptible tubers. Stubby root nematodes transmit tobacco rattle virus (TRV), the causal agent for corky ringspot disease (CRS) of potato. CRS disease was maintained in soil when hairy nightshade was present in rotation crops of alfalfa or Scotch spearmint that otherwise eliminated the disease. Hairy nightshade also is a host of potato leaf roll virus (PLRV), which is transmitted by green peach aphids (GPA). GPA preferentially land and readily reproduce on hairy nightshade. Aphid transmission of PLRV from hairy nightshade to potato was four times greater than the virus transmission rate from potato to potato. Integrated management of these potato nematodes, diseases, and insect pests also should include strategies to control hairy nightshade in potato and rotation crops. Nomenclature: Columbia root-knot nematode—race 1, Meloidogyne chitwoodi Golden et al; green peach aphid, Myzus persicae (Sulzer); hairy nightshade, Solanum sarrachoides Sendtner SOLSA; northern root-knot nematode, Meloidogyne hapla Chitwood; stubby root nematode, Paratrichodorus allius Jensen; alfalfa Medicago sativa L.; potato, Solanum tuberosum L.; Scotch spearmint, Mentha cardiaca Baker.

Weed Hosts of Paratrichodorus allius and Tobacco Rattle Virus in the Pacific Northwest

The ability of several weed species to serve as hosts for tobacco rattle virus (TKV), the causal agent of corky ringspot disease of potato (CRS), and its nematode vector,Paratrichodorus allius, was investigated in greenhouse studies. ViruliferousP. allius multiplied on 24 out of 37 weed species tested, indicating they were suitable hosts of the vector. However, only 11 of these weeds were infected with TRV, as determined by ELISA. The nonhost status of a given weed species was not changed whether the viruliferous vector population originated from CRS problem fields in WA, OR, or ID. Several weeds served as hosts for the vector and virus including kochia, prickly lettuce, henbit, nightshade species (black, hairy, and cutleaf), common chickweed, and annual sowthistle. Virus-freeP. allius acquired TRV from the three nightshade species, volunteer potato grown from TRV-infected tubers, and prickly lettuce, and subsequently transmitted the virus to ‘Samsun NN’ tobacco indicator plants. Thus, some weeds may play a role in the epidemiology of CRS by perpetuating TRV and its vector in a problem field.ResumenLa capacidad de diversas especies de malezas para servir como hospedante del virus rattle del tabaco (TRV), agente causal de la enfermedad de papa conocida como anillo corchoso (CRS) y de su vector, el nematodoParatrichodorus allius ha sido investigada en estudios de invernadero. ElP. allius se multiplicó en 24 de las 37 especies de malezas probadas, lo cual indica que son hospedantes apropiados del vector. Sin embargo, solamente 11 de estas malezas se infectaron con TRV de acuerdo a la determinación por el método ELISA. La condición de no hospedante de una especie dada de maleza no cambió aún en el caso de que la población del vector virulífero se hubiera originado en campos con problema de CRS de WA, OR, o ID. Diferentes malezas sirvieron como hospedante del vector y del virus incluyendo cochia-alfalfa, escarola, henbit, especies de hierba mora (negra, pilosa y de hoja cortada), hierba pajarera común y lechuguilla silvestre anual.P. allius libre de virus adquirió el TRV de las tres especies de hierba mora, de las plantas voluntarias de papa provenientes de tubérculos infectados y de la escarola y subsequentemente transmitió el virus a las plantas indicadoras de tabaco Sansum NN’. Es así como algunas malezas pueden jugar un rol en la epidemiología del CRS, perpetuando el TRV y su vector en un campo problema.

Pathogenicity of Washington and Oregon isolates of tobacco rattle virus on potato

Soil samples from corky ringspot (CRS) problem fields of potato in the states of Washington and Oregon were collected and planted withNicotiana tabacum ‘Samsun NN’ tobacco to bait tobacco rattle virus (TRV) and to increaseParatrichodorus allius populations, the vector of TRV. Pathogenicity of three isolates of TRV was assessed on Russet Burbank and Russet Norkotah plants usingP. allius as the vector. The most severe CRS tuber symptoms were with TRV from Pasco, WA, followed by Umatilla, OR, and Mattawa, WA, indicating a distinct variation in virulence among virus isolates. The lowest number ofP. allius that transmitted TRV resulting in CRS symptoms on Russet Norkotah was three nematodes per 250 cm3 soil. When potato plants were exposed toP. allius at different times in their growth, tubers on older plants were more resistant than younger tubers to CRS. Severity of CRS tuber symptoms was correlated with age of potato plants in pot culture. Reproduction ofP. allius on potato roots did not influence the incidence and severity of tubers symptoms. Under similar conditions, Bintje, a variety known to be resistant to CRS, served as a host forP. allius, yet remained asymptomatic. The protocol employed in these studies is appropriate for testing potato germplasm for resistance to CRS.

Hairy Nightshade is an Alternative Host of Spongospora subterranea, the Potato Powdery Scab Pathogen

Root galls possibly caused by Spongospora subterranea were observed on hairy nightshade (Solanum sarrachoide; HNS). HNS galls and galls from potato were used to artificially inoculate potato and HNS. Eighty-three and 52% potato and HNS plants inoculated with potato inoculum had root galls, respectively. Ten and 31% potato and HNS plants inoculated with HNS inoculum had root galls, respectively. A S. subterranea-specific PCR significantly correlated (Pu2009<u20090.0001, Phi Coefficientu2009=u20090.69) with visual assessment of gall incidence in 34 of 40 samples. Five of 40 samples had no galls, but gave positive PCRs. One of 40 samples had root galls, but gave a negative PCR. More sporosori were produced on potato than on HNS. Therefore, the root galls on HNS were caused by S. subterranea that is able to complete its life cycle on HNS and produce new generations of sporosori that are infectious on potato.ResumenAgallas de la raíz, posiblemente causadas por Spongospora subterranea fueron observadas en belladona vellosa (Solanum sarrachoide; HNS). Agallas de HNS y de papa fueron utilizadas para inocular artificialmente papa y HNS. El 83% y el 52% de plantas de papa y HNS inoculadas con inóculo de papa tuvieron agallas de la raíz respectivamente. El 10% y 31% de plantas de papa y HNS inoculadas con inóculo de HNS tuvieron agallas de la raíz respectivamente. Un PCR especifico para S. subterranea correlacionó significativamente (Pu2009<u20090.0001, Coeficiente Phiu2009=u20090.69) con evaluación visual de incidencia de agallas en 34 de 40 muestras. Cinco de 40 muestras no tuvieron agallas pero dieron PCR positivo. Una de las 40 muestras tuvo agallas de la raíz pero dio PCR negativo. Más sporosori fue producido en papa que en HNS. Por lo tanto las agallas de la raíz en HNS fueron causadas por S. subterranea que es capaz de completar su ciclo de vida en HNS y producir nuevas generaciones de sporosori que son infecciosas en papa.

Impact of wheat and corn as rotational crops on corky ringspot disease of Russet Norkotah potato

Tobacco rattle virus (TRV), the causal agent of corky ringspot disease of potato (CRS), was detected by reverse transcription-polymerase chain reaction (RT-PCR) in root tissues of field- and greenhouse-grown wheat (two) and corn (10) cultivars. TRV was also detected in some of the same samples by enzyme-linked immunosorbent assay (ELISA), but in a low frequency. Compared to ‘Samsun NN’ tobacco, wheat and corn appeared to be poorer hosts of TRV. However, these crops served as inoculum reservoirs of TRV. A nonviruliferous population of the nematodeParatrichodorus allius, the vector of TRV, acquired the virus from infected wheat and corn roots, and transmitted it to potato. ‘Russet Norkotah’ potatoes grown following TRV-infected corn and wheat, were blemished with arcs, concentric rings and diffuse browning, characteristic symptoms of CRS. The observations presented here suggest that wheat and corn as rotational crops will sustain TRV in a CRS problem field and the virus may cause severe damage on subsequent potato crops.ResumenEl virus “rattle” del tabaco (TRV en inglés), agente causal de la enfermedad de la papa denominada mancha de anillo corchosa (CRS), fue detectado por transcriptión inversa de la reacción en cadena de la polimerasa (RT-PCR) en el tejido de las raíces de dos cultivares de trigo y diez cultivares de maíz cultivados en campo y en invernadero. El TRV también fue detectado en algunas de las mismas muestras mediante el ensayo de inmunoabsorción con conjugados enzimáticos (ELISA), pero en baja frecuencia. Comparado con el tabaco de la variedad “Samsun NN”, el trigo y el maíz parecen ser hospederos más precarios de TRV. Sin embargo, esos cultivos sirvieron como reservorios de inóculos de TRV. Una población no virulenta del nematodoParatrichodorus allius, el vector del TRV, adquirió el virus de las raíces infectadas de trigo y maiz, y lo transmitió a la papa. Las papas de la variedad “Russet Norkotah” que crecieron a partir de la infestatión del TRV al maíz y trigo, estuvieron manchadas con arcos, anillos concéntricos y presentaron color marrón difuso, sintomas característicos de CRS. Las observaciones que aquí se presentan sugieren que el trigo y el maíz como cultivos de rotación mantendrán el TRV como un problema de campo, pudiendo este virus causar daños severos en los subsiguientes cultivos de papa.

Population Dynamics of the Beet Leafhopper in Northeastern Oregon and Incidence of the Beet Leafhopper-Transmitted Virescence Agent Phytoplasma

Beet leafhoppers were collected weekly on yellow sticky traps placed at 36 locations in Morrow and Umatilla Counties in northeastern Oregon in April through November 2007, 2008, and 2009. Insects were counted, collected, and a subset of the insects was tested for the presence of the beet leafhopper-transmitted virescence agent phytoplasma, the causal agent of potato purple top disease in this region. Beet leafhoppers were present throughout the sampling period and the number of insects collected peaked in June of each year with smaller peaks in July and October. Of the 804 insects tested for phytoplasma in 2007, 2008, and 2009, 21, 18, and 22% tested positive for phytoplasma, respectively. Most of the phytoplasma-positive insects were collected from mid-June through July. Positive insects, however, were collected as late as 13 November in 2007 and 2008. These data indicate that a relatively high proportion of the beet leafhoppers in this area are harboring the phytoplasma. Therefore, the potential for development of purple top disease of potatoes from migrating beet leafhoppers in this important potato producing region is quite high and measures to control this pest throughout the growing season are probably necessary in order to reduce disease pressure.ResumenSe colectaron chicharritas de la remolacha semanalmente en trampas amarillas pegajosas ubicadas en 36 localidades en los Condados de Morrow y Umatilla en el noreste de Oregon desde abril hasta noviembre de 2007, 2008 y 2009. Se contaron los insectos, se colectaron y se probó un sub-juego de ellos para la presencia del fitoplasma, agente de la virescencia transmitido por la chicharrita de la remolacha, que es el agente causal de la enfermedad de la punta morada de la papa en esta región. Las chicharritas de la remolacha estuvieron presentes a lo largo del período del muestreo y el número de insectos colectados alcanzó un máximo en junio de cada año con pequeños picos en julio y octubre. De los 804 insectos probados para fitoplasma en 2007, 2008 y 2009, 21, 18 y 22% fueron positivos para el fitoplasma, respectivamente. La mayoría de los insectos positivos se colectaron desde la mitad de junio y todo julio. No obstante, se colectaron positivos hasta tan tarde como el 13 de noviembre de 2007 y 2008. Estos datos indican que una alta proporción relativa de las chicharritas de la remolacha en esta área están manteniendo al fitoplasma. De aquí que el potencial de desarrollo de la enfermedad de la punta morada de la papa proveniente de chicharritas migratorias en esta región tan importante en la producción de papa es muy alto y las medidas de control de esta plaga a lo largo del ciclo de cultivo son probablemente necesarias a fin de reducir la presión de la enfermedad.

Characterization of Beet curly top virus Strains Circulating in Beet Leafhoppers (Hemiptera: Cicadellidae) in Northeastern Oregon

The beet leafhopper, Circulifer tenellus, is an agriculturally important pest, particularly in the western United States. This insect transmits the Beet curly top virus (BCTV) to multiple crops, including bean, tomato, and pepper. In this study, we investigated the incidence of BCTV in individual leafhoppers collected at several sites in northeastern Oregon during the growing season in 2007, 2008, and 2009. Of the 800 insects tested, 151 (18.9%) were found positive for the virus. Percentage of virus incidence varied from 0% at one location in 2009 to a high of 55.6% for a location sampled in 2008. The complete virus genomes from one virus-positive insect collected in each of the 3 years were determined. BLAST analysis of the BCTV whole-genome sequences from 2007, 2008, and 2009 insects showed 98, 94, and 96% identities with the BCTV-Worland sequence (AY134867), respectively. The BCTV_2008 sequence showed the greatest identity (96%) with another BCTV genomic sequence (JN817383), and was found to be a recombinant between the BCTV-Worland type, representing the majority of the genome (approximately 2.2 kb), and the BCTV-CFH type that provided an approximately 0.8-kb fragment spanning replication-related genes C1 and C2. This area of the BCTV genome, between the C1 and C2 genes, was previously found to carry symptom determinants of the virus, and the data may suggest more severe effects of BCTV during the 2008 season. Results indicate that BCTV is common and widespread in C. tenellus in eastern Oregon and that there is substantial genetic diversity among the virus strains present in this important field and vegetable crop-growing region.

Characterization of Resistance to Corky Ringspot Disease in Potato : A Case for Resistance to Infection by Tobacco Rattle Virus

Corky ringspot disease (spraing) is incited by the tobacco rattle virus (TRV) transmitted by stubby root nematode (Paratrichodorus spp.). The resulting damage consists of internal and skin surface necrotic blemishes which render the tubers unmarketable. Resistance to the disease has been extensively documented in breeding programs. High levels of resistance are known for a number of varieties and breeding lines. Because tubers that are symptomless but virus infected have been documented, the nature of resistance is a point of debate. In two field locations where a total of 1,259 tubers of resistant breeding lines were RT-PCR tested, 5.6 and 2.0% of symptomless tubers gave positive PCR tests in the different fields. Nearly all of these were from three clones that would have been classified as susceptible by symptoms in later testing. Taken as a whole 58% of the symptomatic tubers gave positive PCR tests. Standard commercial susceptible cultivars showed 34% symptomless tubers with positive PCR results. We have shown here that tubers of most resistant lines are not positive for the virus when asymptomatic tubers are tested by RT-PCR, while symptomatic tubers are mostly positive. Within selected resistant materials, clones with the highest level of asymptomatic positives also showed susceptible responses as assessed by visual ranking in later tests. Although RT-PCR fails to amplify from symptomatic tubers in some cases, the results of this study suggest that most resistant breeding lines do not test positive as latent carriers of the virus. Therefore, lack of symptoms appears to be an expression of resistance to infection by TRV.ResumenLa mancha de anillo corchoso (torsión) en papa es causada por el virus del tobacco rattle (TRV) y trasmitido por el nematodo de la raíz gruesa (Paratrichodorus spp.). El daño consiste en manchas necróticas internas y superficiales de la piel, las cuales convierten a los tubérculos en no comerciables. La resistencia a la enfermedad ha sido extensamente documentada en los programas de mejoramiento. Se conocen altos niveles de resistencia para algunas variedades y líneas de mejoramiento. Debido a que tubérculos infectados que carecen de síntomas han sido documentados, la naturaleza de la resistencia es un punto en debate. En campos de dos localidades donde un total de 1,259 tubérculos de líneas resistentes de mejoramiento fueron probados por RT-PCR, 5.6% y 2% de los tubérculos sin síntomas dieron positivo en los campos diferentes. Casi todos ellos provinieron de tres clones que podían haber sido clasificados susceptibles en la prueba posterior. Tomando como un todo el 58% de tubérculos sintomáticos dieron positivo en las pruebas PCR. El 34% de tubérculos comerciales comunes de cultivares susceptibles no mostraron síntomas a pesar de los resultados positivos con PCR. Hemos demostrado que los tubérculos de líneas más resistentes no dan positivo para el virus cuando los tubérculos asintomáticos son probados por RT-PCR, mientras que los sintomáticos son en su mayoría positivos. Dentro de los materiales resistentes seleccionados, los clones con niveles altos de positivos asintomáticos también mostraron respuesta positiva cuando se evaluaron por medios visuales en las pruebas posteriores. Aunque la prueba RRT-PCR no logra amplificar en algunos casos los tubérculos sintomáticos, los resultados de este estudio sugieren que las líneas de mejoramiento más resistentes no dan positivo como portadores latentes del virus. Por lo tanto, la falta de síntomas parece ser una expresión de resistencia a la infección del TRV.