Ekaterini Riga

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.

Potential use of arugula (Eruca sativa L.) as a trap crop for Meloidogyne hapla

Summary – In the absence of resistant cultivars, the impending loss of methyl bromide (MBr) and few sustainable alternatives available, managing the northern root-knot nematode, Meloidogyne hapla, is a challenge in temperate vegetable and nursery production systems. Many brassica plants, including arugula, Eruca sativa, possess biofumigant and trap crop qualities, and thus have been gaining popularity as potential alternatives to MBr. As part of a project to develop alternatives to MBr, this study was conducted to determine the effects of arugula cv. Nemat on three glasshouse populations of M. hapla from Rhode Island (RI), New York, Geneva (NYG) and Michigan (MI). In two glasshouse experiments conducted at 20 ± 2 ◦ C and 28 ± 2 ◦ C, arugula and Rutgers tomato (standard susceptible) seedlings were inoculated with either 0 (control) or 3000 eggs of 67-85% undifferentiated stages of the three populations. Experiment 1 was terminated at 20 days and Experiment 2 at 28 days after nematode inoculation. At 20 ◦ C, 200 and 280 degree-days (DD, base 10 ◦ C) were accumulated, while 360 and 504 DD were accumulated at 28 ◦ C in the respective experiments. Total numbers of nematodes recovered from roots varied by host and by nematode population over the course of the study, but the numbers of females in roots did not vary significantly. This suggests variability in reaching the adult female stage. Egg and egg mass production was normal in all nematode-infected tomatoes, but no eggs were produced in more than 80% of arugula plants, and less than 17% of the arugula samples had fewer than five loose eggs and no egg masses. The results show that arugula interferes with development and reproduction of populations of M. hapla and thus has potential as a trap crop to control M. hapla.

Molecular identification of two stubby root nematode species

Stubby root nematodes are of increasing importance to the potato industry in the Pacific Northwest (PNW) of the USA as they transmitTobacco rattle virus (TRY), the causal agent of corky ringspot disease. In the PNW,Paratrichodorus allius is the most prevalent TRV vector nematode species in potato growing areas. A closely related species,P. teres, is also found in parts of the PNW.P. allius andP. teres are morphologically similar, thus creating problems for routine identification. Few studies have utilized molecular techniques to identify species belonging to the Trichodoridae. Species-specific reverse PCR primers for bothParatrichodorus species were designed and located in the ITS-1 rDNA region and used in combination with a universal nematode forward primer located in the 18S rDNA. Primer reliability was confirmed byin vitro screening of differentP. allius populations andin silico analysis ofP. teres on the respective target species. Furthermore, specificity was demonstrated by the absence of cross-reactions with a range of common plant-parasitic nematode species typical of potato growing areas in the PNW. A duplex PCR test was developed that was effective for simultaneous detection of both targetParatrichodorus species.ResumenLos nematodos que causan la raíz tocón son de creciente importancia para la industria papera en el Pacífico Noroeste (PNW) de EUA porque transmiten elTobaccorattle virus (TRV), agente causal del anillo corchoso. En el PNW, elParatrichodorus allius es el más importante vector del TRV en las áreas de cultivo de papa. También está presente en ciertas partes del PNWP. teres, una especie relacionada.P. allius yP. teres son morfológicamente similares, por lo que crean problemas para una identificación de rutina. Algunos estudios han utilizado técnicas moleculares para identificar las especies pertenecientes a los Trichodoridae. Los iniciadores de PCR en reversa, específicos para ambas especies deParatrichodorus han sido diseñados y localizados en la región ITS-1 rADN y usados en combinación de un iniciador en la región 18S rADN. La confiabilidad del iniciador fue confirmada en un tamizadoin vitro de diferentes poblaciones deP. allius y en análisisin silico deP. teres, sobre las respectivas especies objetivo. Más aún, la especificidad fue demostrada por ausencia de reacciones cruzadas con una gama de especies de nematodos parásitos de plantas típicas de las áreas de cultivo de papa en el PNW. Ha sido desarrollada una prueba de PCR doble que fue más efectiva para la detección de simultánea de ambas especies deParatrichodorus.

Evidence for the influence of weeds on corky ringspot persistence in alfalfa and Scotch spearmint rotations

Corky ringspot disease (CRS) of potato is caused by tobacco rattle virus (TRV). The virus is transmitted by the stubby root nematode (Paratrichodorus allius) in the Pacific Northwest potato-producing regions. Alfalfa (Medicago sativa L.) and Scotch spearmint (Mentha cardiaca Baker) rarely serve as hosts for TRV. Therefore,P. allius reared on these plants for 1 to 3 months are cleansed of TRV in greenhouse trials. However, weeds in alfalfa and Scotch spearmint rotation crops may serve as hosts for the virus. In greenhouse trials, hairy nightshade (Solanum sarrachoides), prickly lettuce (Lactuca serriola), henbit (Lamium amplexicaule) and, green foxtail (Setaria viridis) grown alone were found to be suitable hosts ofP. allius, whereas Powell amaranth (Amaranthus powellii) was not. ViruliferousP. allius added to hairy nightshade, prickly lettuce, henbit, green foxtail, or Powell amaranth in mixtures with alfalfa and/or Scotch spearmint occasionally remained viruliferous over a 3-to 4-month period, whereasP. allius maintained on weed-free alfalfa or Scotch spearmint became virus-free after 1 to 2 months. Potato grown in soil containingP. allius that had been maintained on weed-alfalfa or weed-Scotch spearmint mixtures for 3 to 4 months exhibited slight to severe CRS symptoms on new tubers, whereas potato following weed-free Scotch spearmint or alfalfa were free from CRS symptoms. Severe CRS symptoms on potato tubers were only observed when potatoes were grown in soil containingP. allius that were maintained on hairy nightshade or hairy nightshade mixtures with alfalfa or Scotch spearmint. These preliminary data suggest that the presence of weeds that serve as hosts of both TRV and P.allius may nullify the positive effects of growing alfalfa or Scotch spearmint for CRS control. Targeted control efforts of known weed hosts may be required to successfully eliminate CRS from fields using alfalfa and Scotch spearmint rotational crops.ResumenEl anillo corchoso de la papa (CRS) es causado por el tobaco rattle virus (TRV). El virus es transmitido por el nematodo de la raiz (Paratrichodorus allius) en regiones productores de papa del noroeste del Pacífico. La alfalfa (Medicago sativa L.) y menta escocesa (Mentha cardiaca Baker) rara vez sirven de hospedante para el TRV. Por lo tanto, en pruebas de crianza deP. allius en invernadero, en estas plantas por 1 a 3 meses sirvió para limpiarlo de TRV. Sin embargo, las malezas de los cultivos de rotación menta escocesa y alfalfa pueden servir como hospedantes para el virus. En pruebas de invernadero se encontró que la hierba mora (Solanum sarrachoides), la lechuga escarola (Lactuca serriola), la ortiga (Lamium amplexicaule) y el almorejo (Setaria viridis) crecidos separadamente son huéspedes apropiados deP. allius, mientras que el amaranto Powell (Amaranthus powellii) no se infectó. ElP. allius virulífero colocado en hierba mora, escarola, ortiga, almorejo o amaranto Powell en mezclas con alfalfa y/o menta escocesa, permanecieron ocasionalmente virulíferos por un periodo de 3 a 4 meses mientras que elP. allius mantenido en alfalfa o en menta escocesa libres de malezas, liegó a liberarse del virus después de 1 a 2 meses. Tubérculos nuevos de papa cultivada en suelos conteniendoP. allius que había sido mantenido sobre mezclas de malezas-alfalfa o de malezas-menta escocesa por 3 a 4 meses, mostraron ligeros a severos síntomas de CRS, mientras que la papa sembrada después de menta escocesa o de alfalfa libres de malezas no mostraron síntomas de CRS. Se observaron síntomas severos de CRS en tubérculos solamente cuando se sembró papa en terrenos que conteníanP. allius mantenido en hierba mora o en mezclas de hierba mora con alfalfa o menta escocesa. Estos datos preliminares sugieren que la presencia de malezas que sirven como hospedantes tanto del TRV como del P.allius pueden anular los efectos positivos de sembrar alfalfa o menta escocesa para controlar CRS. Para eliminar exitosamente el CRS de los campos puede ser necesario hacer determinados esfuerzos orientados a eliminar las malezas que son huéspedes conocidos utilizando alfalfa y menta escocesa como cultivos de rotatión.

First report of the stubby-root nematode, Paratrichodorus teres, from potato in the Columbia Basin of Washington State.

Stubby-root nematodes of the genus Paratrichodorus are migratory ectoparasites that cause stunted and deformed roots. They also transmit Tobacco rattle virus, the causal agent of corky ringspot disease in potato. Thus, they are important to the potato industry in the Pacific Northwest, including the Columbia Basin of Washington state, which is one of the largest potato-producing regions in the United States. Stubby-root nematode species are difficult to identify because the morphological differences between the species are very small (4). Paratrichodorus teres is a morphologically similar species and has been reported mainly from temperate regions within Europe. P. teres has also been reported in potato fields in eastern Oregon (3). The morphological similarity between P. allius and P. teres creates problems for routine identification because trichodorid species have a conservative morphology and are separated by the following primary characteristics: females, type of genital system and vulva position; males, number of ventromedian precloacal supplements and cervical papillae and habitus (2). As with most soil nematodes, females are more prevalent than the males. Unfortunately, in the generic key (2), female P. allius and P. teres belong to subgroup 1-12 and are separated by a secondary characteristic, vaginal shape that could be affected by fixation or handling. Male P. allius and P. teres are separated by the former species having one fewer ventromedian precloacal supplement. Thus, the morphological similarity between P. allius and P. teres creates problems for routine identification. This might be one of the reasons that P. teres has not been diagnosed in Washington until now. Using nematode morphological diagnostic keys (1,2) and comparing 18S rDNA sequence data obtained from specimens with those listed on public sequence databases, e.g., NCBI GenBank, stubby-root nematodes from two potato fields close to Moses Lake, Grant County, WA, were diagnosed as P. teres. The two adjacent potato fields are irrigated and are situated approximately 100 miles from the eastern Oregon site where P. teres was first described (3). Soil samples were collected from several Columbia Basin potato fields that had corky ringspot disease and stubby-root nematodes. Corky ringspot disease is an emerging disease in Washington, and the presence of a new viruliferous nematode species might be of concern to the potato industry. References: (1) W. Decraemer. Page 615 in: Manual of Agricultural Nematology. W. R. Nickle, ed. Marcel Dekker, Inc., New York, 1991. (2) W. Decraemer and P. Baujard. Fundam. Appl. Nematol. 21:37, 1998. (3) H. J. Jensen et al. Plant Dis. Rep. 58:269, 1974. (4) S. MacFarlane et al. Adv. Bot. Res. 36:169, 2002.

Hairy nightshade undermines resistance of potato breeding lines to columbia root-knot nematode

Columbia root-knot nematode,Meloidogyne chitwoodi, is a major pest of potato in the Pacific Northwest of the USA and is controlled by costly soil fumigation. Potato breeding lines have been developed with resistance to the predominant race 1 (CRKN-1) ofM. chitwoodi. Hairy nightshade,Solanum sarrachoides, is a common weed in potato production in the western USA and a host of CRKN-1. Greenhouse and field studies were conducted with two potato lines with known CRKN-1 resistance (PA95B4-67 and PA99N82-4) and a CRKN-1 susceptible potato cultivar, Russet Burbank. Very little or no CRKN-1 reproduction took place in roots of both resistant breeding lines, and only minor tuber infection occurred when grown in the absence of hairy nightshade. However, when resistant lines were grown in the presence of hairy nightshade, some PA95B4-67 tubers were infected, whereas PA99N82-4 expressed tuber resistance. Hairy nightshade grown with potato maintained CRKN-1 populations prior to potato tuber set, allowing nematodes to infect developing tubers lacking resistance. PA99N82-4 grown in the presence of CRKN-1 and hairy nightshade produced tubers free of CRKN-1 damage, indicating both root and tuber resistance to CRKN-1. Russet Burbank tubers were damaged by CRKN-1 regardless of hairy nightshade presence. These results demonstrate how weed hosts of CRKN-1 may negate the positive impact of growing CRKN-1 resistant potatoes that lack tuber resistance, and the importance of weed control on managing plant parasitic nematode populations.ResumenEl nematodo del nudo de la raíz de Columbia,Meloidogyne chitwoodi, es una importante plaga de la papa en el Pacífico Noroeste de USA y es controlado con costosas fumigaciones. Se han desarrollado líneas de mejoramiento con resistencia a la predominante raza 1 (CRKN-1) deM. chitwoodi. La hierba mora vellosaSolanum sarrachoides, es una maleza común en la producción de papa en el oeste de USA y es un hospedero de CRKN-1. Se realizaron estudios en invernadero y en campo con dos líneas de papa con conocida resistencia al CRKN-1 (PA95B4-67 y PA99N82-4) y el cultivar susceptible, Russet Burbank. Hubo poca o ninguna reproducción de CRKN-1 en las raíces de ambas líneas de mejoramiento y solamente se produjeron infecciones menores cuando se cultivó en ausencia de hierba mora. Sin embargo, cuando se cultivaron líneas resistentes en presencia de hierba mora, algunos tubérculos de PA95B4-67 fueron infectados, mientras que PA99N82-4 expreso resistencia de tubérculos. La hierba mora que creció conjuntamente con papa, mantuvo las poblaciones de CRKN-1 antes de la tuberización de la papa, permitiendo que los nematodos infecten los tubérculos en crecimiento faltos de resistencia. PA99N82-4 creciendo en presencia de CRKN-1 y de hierba mora produjo tubérculos libres de daño por CRKN-1, indicando resistencia de raíces y tubérculos al CRKN-1. Los tubérculos de Russet Burbank recibieron daño de CRKN-1 a pesar de la presencia de hierba mora. Estos resultados demuestran como las malezas hospedantes de CRKN-1 pueden invalidar el impacto positivo de cultivar papa resistente al CRKN-1 pero que no tienen resistencia en el tubérculo y la importancia del control de malezas para el manejo de poblaciones de nematodos parásitos de plantas.

Evaluation of Marigolds and Entomopathogenic Nematodes for Control of the Cabbage Maggot Delia radicum

The susceptibility of Delia radicum, cabbage maggot (CM), first instar larvae to fresh tissue extracts of two marigolds (Tagetes erecta and T. patula), the entomopathogenic nematode Steinernema feltiae, and a combination of them, was evaluated under laboratory and glasshouse conditions. In the laboratory, CM larvae were susceptible to marigold fresh tissue extracts; the root extracts were the most effective. Fresh root tissue extracts of non-flowering and flowering T. erecta caused 28% and 84% CM mortality, and T. patula caused 65% and 100% CM mortality, respectively. The nematodes caused up to 46% CM mortality at a concentration of 300 IJs/larva. In the glasshouse, up to 95% reduction of CM was achieved when cabbage plants, infected with CM eggs, were treated with fresh root extracts from either Tagetes species. Combination treatments with Tagetes and S. feltiae were also effective. Fresh tissue extracts of Tagetes spp. and S. feltiae show potential as control agents of D. radicum.

A New Pathotype of Meloidogyne chitwoodi Race 1 from Washington State

Meloidogyne chitwoodi Golden et al. is a serious pest of potato (Solanum tuberosum L.), and is widespread in the Pacific Northwest United States. M. chitwoodi is currently reported to consist of two host races and one pathotype (2,3) that are not distinguished morphologically. Host race 1 reproduces on Chantenay carrot but not on Thor alfalfa and host race 2 reproduces on alfalfa but not on carrot. Both races fail to reproduce on roots of S. bulbocastanum, a wild potato species used as a source of resistance in our breeding program (1). The resistance to race 1 in S. bulbocastanum is attributed to Rmc1(blb) gene. Pathotype 1 of race 2 breaks resistance and reproduces on S. bulbocastanum (2). We have tested resistant breeding lines repeatedly in Prosser, WA field plots infested with MC race 1 and harvested tubers free from M. chitwoodi damage. In 2004 however, tubers of some resistant lines were damaged by the M. chitwoodi population that did not cause damage in the past. Populations of M. chitwoodi were established on tomato by adding peels obtained from the infected tubers of resistant lines. The reproductive factor, final number of eggs ÷ initial inoculum, of the new population was determined on five replications of 3-week-old Chantenay carrot and Thor alfalfa. Five thousand eggs were extracted from nematode cultures reared on tomatoes and then were added around the root system of the test plants. The plants were maintained in the greenhouse for 55 days before the nematode eggs were extracted and RF (reproductive factor = final/initial population) values determined. Like the MC race 1, new populations reproduced on Chantenay carrot (RF > 1) but failed to reproduce on Thor alfalfa (RF < 0.1). Unlike MC race 1, the new populations reproduced on roots of all breeding lines that carried Rmc1(blb) gene (RF > 1). These results suggest that the selected population of M. chitwoodi in the Prosser site is a new pathotype, which is designated pathotype 1 of MC race 1. References: (1) C. R. Brown et al. Am. J. Potato Res. 83:1, 2006. (2) H. Mojtahedi et al. J. Nematol. 30:506, 1998. (3) G. S. Santo et al. Plant Dis. 69:361, 1985.