J. R. Davis

Verticillium wilt of potato: a model of key factors related to disease severity and tuber yield in Southeastern Idaho

In three years (1994, 1995, and 1996), a total of 100 commercial potato fields in southeastern Idaho were surveyed for soil variables, severity of Verticillium wilt, soil inoculum density ofVerticillium dahliae andColletotrichum coccodes, colonization of stems, root, and tubers byV. dahliae andC. coccodes, and tuber yield, size, and quality. As a generalization, factors related to soil integrity (organic matter, organic nitrogen, and increased nutrient availability) were most closely related to wilt suppression and higher tuber yields, whereas factors related to loss of soil integrity (sodium and reduced nutrient availability) were related to increased wilt and lower tuber yields. In a multiple regression analysis, three independent variables, feeder-root infections byV. dahliae, sodium content in soil, and soil organic content, were significant predictors of tuber yield. With these three factors, this model accounted for 49%, 53%, and 62% of the field variability related to total yield in 1994, 1995, and 1996, respectively. Throughout this investigation,V. dahliae root infections had the most direct effect on tuber yield, which emphasizes the importance of quantifying root infections in epidemiological studies of Verticillium wilt. Based on these results, organic matter may be one factor that can be manipulated for suppression of Verticillium wilt without reducing soil populations of the pathogen.

Approaches to control of potato early dying caused byVerticillium dahliae

Potato early dying disease, caused byVerticillium dahliae, may be either suppressed or controlled by a variety of procedures. These methods include the growing of resistant cultivars, attention to cultural management, utilization of pesticides, and solar heating of soils. The greatest successes in control of Verticillium wilt have been achieved with the use of either soil fumigants or clonal resistance, but these approaches have been restricted. Widespread use of fumigants has been limited by cost, and the lack of commercial acceptance has often restricted the utilization of resistant potato cultivars. The Katahdin and Targhee cultivars are currently available with resistance and/or tolerance to this disease. The Russet Burbank potato also possesses a limited degree of resistance to the fungus, and with this resistance, the disease appears to be suppressed by optimal growing conditions. In potato fields that have been cropped for several years, disease suppression in Russet Burbank was found to be related to methods of irrigation and increased nitrogen availability. It is suggested that improved utilization of resistant germplasm and effective use of biological control strategies may ultimately lead to economical control of this disease.ResumenLa enfermedad de la muerte prematura de la papa, causada porVerticillium dahliae, puede ser eliminada o controlada por varios procedimientos. Estos métodos comprenden el cultivo de cultivares resistentes, atención prestada al manejo del cultivo, utilizatión de insecticidas y fungicidas y el calentamiento solar de los suelos. Los más grandes éxitos en el control de la marchitez por Verticillium se han logrado mediante el uso de fumigantes de suelos o resistencia clonal, pero estos métodos han sido restringidos. La aplicación amplia de fumigantes ha sido limitada por el costo y, a menudo, la falta de aceptación comercial ha restringido la utilización de cultivares resistentes de papa. Los cultivares Katahdin y Targhee están actualmente disponibles con resistencia o tolerancia a esta enfermedad, o con la combinación de ambas. Russet Burbank también tiene un grado limitado de resistencia al hongo y, con esta resistencia, la enfermedad parece ser vencida mediante condiciones óptimas de cultivo En los campos de papa que han sido cultivados durante varios años, se encontró que la eliminación de la enfermedad en Russet Burbank estuvo relacionada con los métodos de irrigación y un aumento en la disponibilidad de nitrógeno. Esto sugiere que una utilización mejor del germoplasma resistente y el uso efectivo de las estrategias del control biológico pueden finalmente llevar a un control de esta enfermedad, que sea económico.

Infection of aerial parts of potato plants byColletotrichum coccodes and its effects on premature vine death and yield

Collectotrichum coccodes, the pathogen causing black dot disease of potato, was investigated to determine its potential for causing symptoms on the aerial parts of potato plant, premature vine death, and reduction in yield under greenhouse and field conditions. Spray inoculations with conidial suspensions (106 colony forming units/ml) ofC. coccodes caused sunken, dark, necrotic lesions on stems, leaves and petioles, vein and leaf necrosis, dieback and premature vine death under growth chamber and greenhouse conditions. Field inoculations in 1986 and 1987 provided evidence for an increased incidence of premature vine death in seven potato genotypes (Russet Burbank, Norgold Russet, Superior, Butte, NDA 8694-3, A68113-4 and A66107-51). Late season application of metribuzin at 0.84 kg/ha significantly increased the incidence of stems with black dot symptoms in cv. Russet Burbank at one location. Field inoculations in 1987 at two locations resulted in yield reduction in the late-maturing cv. Russet Burbank (6.3 and 6.5 t/ha) and clone A68113-4 (5.0 t/ha), but not in the early maturing cv. Norgold Russet. Similar results were obtained in greenhouse studies following soil inoculations withC. coccodes: yield reduction was observed in cv. Russet Burbank but not in cvs. Norgold Russet, Superior and Katahdin. Colonization of stem ends of tubers byC. coccodes from spray inoculated field plots was higher than in tubers from uninoculated plots at one of the two locations. These results point to a much broader potential ofC. coccodes as a potato pathogen, than hitherto documented.Colletotrichum coccodes (Wallr.) Hughes (syn.C. atramentarium (Berk. & Br. Taub.) was described in 1825 (21) and has a wide host range (5). Potato and tomato are the more economically important hosts. This fungus has been variously referred to as an unspecialized, minor pathogen or secondary invader (18), weak pathogen (22), specialized parasite (5), or superficial colonizer and widespread epiphyte (19). The symptoms produced by this pathogen on potato have been described as black dot (10, 14) on stems, stolons, tubers and roots, sometimes associated with leaf scorch or wilt (24), rubbery tuber wilt (1), and tuber skin necrosis (17). The fungus is commonly associated with senescent, decaying root and stem tissue, especially at the end of the season. In Idaho, instances of premature death of potato without typical symptoms of Verticillium wilt, but accompanied by a high incidence of stems with black dot symptoms, have been observed in potato crops grown on fields fumigated with metam sodium. Additional observations by growers have also implicated the possible interaction of the herbicide metribuzin with the incidence of black dot. Although it was observed by some workers to accelerate leaf senescence (12, 22), Schmiedeknecht (21) concluded thatC. coccodes was unable to infect the green leaves of potato plant. Even thoughVerticillium dahliae is generally considered the major factor in potato early dying (20), several workers (7, 11, 13, 19, 22) have investigated the possible role ofC. coccodes in causing premature death of potato (8). However, these studies examinedC. coccodes only as a soilborne, root and tuber pathogen of potato; its effects on shoot portions (aerial parts) of the plant were not considered. In addition to causing anthracnose of fruits of tomato, pepper and squash (18), recent reports indicate thatC. coccodes causes foliage blights on eastern black nightshade (2) and velvetleaf (25).The objectives of this study were: (1) to examine the potential ofC. coccodes to cause symptoms on aerial parts of potato plant, (2) to investigate the effect of spray inoculation in the field withC. coccodes on incidence of premature vine death, tuber colonization and yield of potato, and (3) to document the effect of soil inoculation withC. coccodes alone or in combination withV. dahliae on potato varieties under greenhouse conditions.CompendioColletotrichum coccodes, el patógeno causante del punteado negro de la papa, fue investigado para determinar su potencial para producir síntomas sobre las partes aéreas de la planta de papa, muerte prematura del follaje y reducción del rendimiento bajo condiciones de invernadero y de campo. Inoculaciones en forma de aspersión de suspensiones de conidias (unidades formando 106 colonias/cm3) deC. coccodes produjeron lesiones necróticas hundidas y oscuras sobre tallos, hojas y peciolos, necrosis de las nervaduras y de las hojas, muerte descendiente y muerte prematura del follaje bajo condiciones de cámara de crecimiento e invernadero. Inoculaciones de campo en 1986 y 1987 proveyeron evidencia de un incremento en la incidencia de la muerte prematura del follaje en siete genotipos de papa (Russet Burbank, Norgold Russet, Superior, Butte, NDA 8694-3, A68113-4 y A66107-51). Una aplicación de metribuzin al final de la temporada, a razón de 0,84 kg/ha redujo significativamente la incidencia de tallos con síntomas de punteado negro en el cv. Russet Burbank en una localidad. Inoculaciones de campo en dos lugares, en 1987, dieron como resultado una reducción de rendimiento en el cultivar tardío Russet Burbank (6,3 y 6,5 t/ha) y en el clon A68113-4 (5,0 t/ha), pero no en el cultivar precoz Norgold Russet. Resultados similares fueron obtenidos en estudios de invernadero efectuados después de inocular el suelo conC. coccodes: se observó reducción en el rendimiento del cultivar Russet Burbank, pero no en los cultivares Norgold Russet, Superior y Katahdin. La colonización de los extremos apicales de los tubérculos porC. coccodes, en las parcelas de campo inoculadas por aspersión, fue mayor que en los tubérculos de las parcelas no inoculadas en una de las dos localidades. Estos resultados indican queC. coccodes, como patógeno de la papa, tiene un potencial más amplio del conocido hasta el momento.

Fertility and management practices to control verticillium wilt of the russet burbank potato

Management practices for the suppression of Verticillium wilt of Russet Burbank potato include sanitation, use of optimum sprinkler-irrigation practices, soil solarization, and an adequate soil fertility program. Among all cultural factors considered, nitrogen (N) deficiency in potato tissue was most commonly associated with the severity of Verticiilium wilt in Russet Burbank potato. Field studies have shown that increased N availability suppresses Verticiilium incidence on cv Russet Burbank while having no effect on cv Norgold Russet. Studies from both greenhouse and field show that the colonization ofV dahliae in potato stem tissue is suppressed in cv Russet Burbank when the availability of Phosphorous (P) is increased to the optimum. Following one season of cropping with Russet Burbank potato, the treatment providing the optimal N availability also suppressed the increases ofV dahliae populations in the soil during the following year of consecutive cropping. Similarly, after two seasons of continuous potato cropping, treatments with optimal P had lower soil populations ofV. dahliae in soil. Results show the suppression of Verticiilium wilt with optimal fertility.Verticiilium wilt [caused by eitherVerticiilium dahliae Kleb, (microsclerotial form) orVerticiilium albo- atrum Reinke and Berthold (dark mycelial form)] is one of the most severe diseases of potato in the United States. Potato yields, tuber size, and specific gravity may be substantially reduced by this disease, depending on severity, time of occurrence, and growing season.In Idaho and other arid growing regions of the United States, Verticiilium wilt is caused byVerticillium dahliae Kleb. Idaho field studies involving cropping practices, soil fumigation treatments, solarization, and Verticillium-resistant potato clones all support the importance ofV dahliae upon potato yield. Data from these studies show that yield losses due toV. dahliae commonly approximate 5 to 12 metric T/ha (5, 6). Table 1 illustrates the effect of several cropping practices upon relativeV dahliae populations in soil with the effects upon both disease severity and potato yield. With continuous cropping of Russet Burbank,V dahliae populations in soil increased, and yields were reduced by 18 to 19 metric Tlha when compared to locations that had been allowed to remain either weed-free and fallow or where corn had been previously cropped. It was estimated thatV dahliae was influencing yield by about 10 to 12 metric Tlha based on a regression analysis of yield as a function ofV dahliae populations in soil. Similarly, whenV dahliae was suppressed by fumigation treatments involving mixtures of dichloropropene and picfume, yields more significantly increased by 6.5 to 12 metric T/ha (5). Although many factors may influence yields, clones with higher Verticillium resistance than Russet Burbank generally out-yield Russet Burbank. Figure 1 demonstrates the effect of solarization (a technique involving the laying of clear plastic on soil for the purpose of elevating soil temperatures to killV dahliae). When Verticillium was controlled in this manner (lo), there was no significant yield difference between the Russet Burbank potato and the highly resistant A68113-4 clone. The A68113-4 clone grown in non-solarized soil out-yielded the Russet Burbank in non-solarized soil by 31 percent while the solarization treatment significantly increased yield for the Russet Burbank and A68113-4 clones by 46 and 18 percent, respectively. These yield responses were observed in a field where inoculum levels ofV dahliae were relatively low (2.10 cfulgrn of soil). With these losses, the need to develop control procedures is great and to achieve this control the need also exists to accurately evaluate the effect of treatments uponV dahliae. Our Idaho studies have routinely utilized such a procedure (9) in combination with comparisons of both disease severity and yield.

Interactive effects of nitrogen and phosphorus on Verticillium wilt of Russet Burbank potato.

A three-year field study was conducted during 1984–1986 to determine the interactive effects of nitrogen and phosphorus fertilization on Verticillium wilt, and yield and quality of continuously-cropped Russet Burbank potato. The experiment was conducted on a calcareous, silt loam soil with low initial levels of NO3-N (0.9 mg/kg), P (3.5 mg/kg), andVerticillium dahliae (9 cfu/g of soil). The experimental design consisted of a factorial combination of three N treatments (unfertilized check, preplant N or split N) and three P treatments (0,120, or 240 kg P/ha) applied to the same plots during the three-year study. Nitrogen was applied at 0 or 300 kg N/ha in 1984 and 0 or 240 kg N/ha in 1985 and 1986. By the spring of 1986, soil P concentrations for the 0,120, and 240 kg P/ha treatments had increased to 7, 25, and 50 mg/kg and no additional P was applied.In addition to suppressing Verticillium wilt by as much as 95%, N & P treatments also reduced the rate of increase of soilborne inoculum ofV. dahliae. After one season of cropping, the N treatment providing the most efficient N fertilization (300 kg N/ha, split-application) resulted in significantly (p=0.01) lowerV. dahliae counts in soil than the other N treatments. After two seasons of continuous cropping, applying 120 to 240 kg P/ha produced lower populations ofV. dahliae in soil compared to the treatment with no added P. Generally, as N and P treatments approached the highest levels, both wilt incidence andV. dahliae colonization values were reduced.There was a progressive reduction in total yield in nearly all treatments during each year of continuous cropping. Reduction of yield and increased Verticillium wilt incidence was generally greater with N or P deficient plants than with optimally fertilized plants. The highest total and U.S. No. 1 yields and least Verticillium wilt were obtained each year by applying split N and 240 kg P/ha. Results show that optimal N and P can minimize both Verticillium wilt and yield losses that normally occur with intensive potato cropping.

Reaction of potato clones and accessions of Solanum spp. to Verticillium dahliae Kleb. and its toxin.

SummaryThe reaction of 40 potato clones and six accessions ofSolanum spp. to wilt caused byVerticillium dahliae and to the acetone precipitate (AP) of the toxin produced by the pathogen in vitro was studied. There was a highly significant correlation between the wilt reaction of the clones in the glasshouse, the incidence and progress of wilt and severe wilt in the field, and the degree of colonization of stem apices byV. dahliae. Of the clones and accessions evaluated, NDA8694-3, Norgold Russet, BelRus, Superior, Russet Norkotah, Norland andS. demissum were the most susceptible, while A66107-51, A68113-4, Targhee, NDA843-3, Alpha, A7805-8, A7816-14, Russet Nugget,S. chacoense, S. sparsipilum, andS. tarijense were the most resistant to wilt. The reaction of genotypes to the AP ofV. dahliae toxin in an excised leaf bioassay was not correlated with their reaction to Verticillium wilt in the field or glasshouse.

Verticillium wilt resistant potato germplasm: A66107-51 and A68113-4

Potato breeding selections A66107-51 and A68113-4 (Solanum tuberosum gptuberosum) are being released as germplasm that is highly resistant to Verticillium wilt (Verticillium dahliae Kleb.) These selections have been extensively evaluated for resistance to Verticillium as measured by symptom severity and degree of colonization byV. dahliae. They combine outstanding wilt resistance with good tuber maturity characteristics, high yield, and french fry processing tuber type. A66107-51 has long-oblong, russeted tubers, with high yield and variable processing quality. A68113-4 has long-oblong, partially russeted tubers with high yield and good processing quality. Both selections are fertile as female parents, and A66107-51 is occasionally pollen fertile. The Verticillium resistance of these two clones has been transmitted to progeny. These selections were developed by USDA-ARS in cooperation with the Idaho Agricultural Experiment Station. Seed is available from USDA-ARS, Aberdeen, Idaho.CompendioLas selecciones mejoradas de papa A66170-51 y A68113-4 (Solanum tuberosum gptuberosum) están siendo liberadas como germoplasma altamente resistente a la marchitez porVerticillium (Verticillium dahliae Kleb.). Estas selecciones han sido evaluadas extensivamente para resistencia aVerticillium determinada por la severidad de los sintomas y el grado de colonización porV. dahliae. Ellas conbinan una gran resistencia a la marchitez, con buenas características de maduración, alto rendimiento y un tipo de tubérculo apto para el procesamiento como papa frita a la francesa. A66107-51 tiene tubérculos largos y oblangos, rojizos, con alto rendimiento y calidad variable de procesamiento. A68113-4 posee tubérculos largos y oblongos, parcialmente rojizos, con alto rendimiento y buena calidad de procesamiento. Ambas selecciones son fértiles como plantas madres y A66107-51 es ocasionalmente de polen fértil. La resistencia de estos dos clones aVerticillium ha sido transferida a la progenie. Estas selecciones fueron desarrolladas por el Servicio de Investigación Agrícola del Departamento de Agricultura de los Estados Unidos (USDA-ARS) en cooperación con la Estación Experimental Agrícola de Idaho. Los tubérculos-semillas se encuentran disponibles en el USDA-ARS, Aberdeen, Idaho.

Butte: A long Russet potato variety with excellent dehydrating quality

Abstract‘BUTTE’, a new long russet potato variety, was released by the Agricultural Research Service, U. S. Department of Agriculture and the Idaho, Oregon, and Washington Agricultural Experiment Stations in April, 1977. Its tubers are similar to those of ‘Russet Burbank’ but BUTTE offers several advantages to growers and processors. BUTTE has averaged 7% more total yield and 25% more U.S. No. 1’s than Russet Burbank over 51 location-years of testing across southern Idaho, eastern Oregon, and in the Columbia Basin. Its specific gravity in these trials averaged .004 higher than that of Russet Burbank. Dehydrating quality of BUTTE is superior to that of Russet Burbank and the product has longer shelf life. BUTTE french fries well although it accumulates slightly more sugars in storage than does Russet Burbank. Its vitamin C content has averaged 58% higher and protein content 20% higher than that of Russet Burbank. BUTTE is hypersensitive to virus X and resistant to net necrosis. Other disease reactions are similar to those of Russet Burbank.ResumenEl Servicio de Investigación Agrícola del Departamento de Agricultura de los Estados Unidos y las Estaciones Experimentales Agrícola de Idaho, Oregón y Washington, lanzaron en Abril de 1977 una nueva variedad de papa alargada y casposa denominada BUTTE. Sus tubérculos son similares a aquellos de “Russet Burbank” aunque BUTTE ofrece varias ventajas para los agricultores y procesadores. BUTTE tuvo un 7% de mayor rendimiento y 25% más en el grado U.S. N° 1 que “Russet Burbank” en una combinación de pruebas conducidas en 51 localidades/año en el sur de Idaho, al este de Oregón y en la hoya del rió Columbia. En estos experimentes su gravedad especffica promedio fué de .004 más alta que la de “Russet Burbank”. Su calidad para el deshidratado es también superior y el producto tiene una vida más larga. La calidad de BUTTE para papas fritas es buena a pesar de que acumula, en almacenamiento, ligeramente más azúcar que la “Russet Burbank”. Su contenido de vitamina C y proteinas en promedio ha sido 58% y 20% respectivamente, mayor que aquellos de “Russet Burbank”. BUTTE es hipersensible al virus X y resistente a la necrosis en red. Su reacción a otras enfermedades es similar a aquella de “Russet Burbank”.

Some Unique Benefits with Sudangrass for Improved U.S. #1 Yields and Size of Russet Burbank Potato

Three studies provided additional knowledge of beneficial effects of sudangrass for yield and quality increases of the Russet Burbank potato. Two of these studies showed significant increases of both U.S. #1 and smooth tubers > 280 g following green manures of sudangrass. These sudangrass (HS-33) effects did not differ from a sorghum-sudan hybrid (Trudan-8). When a sudangrass green manure was compared with a fallow treatment, results of the first study showed mean yield increases of 36% for U.S. #1 tubers > 280 g and yields of a second study by 34% for U.S. #1 tubers. This same sudangrass treatment outperformed green manures of either Austrian winter pea, barley, or sweet corn by increased U.S. #1 yields that ranged from 27% to 61%. By several lines of evidence, these benefits were found to extend beyond the effect of Verticillium suppression. Soil N was significantly increased following green manures of sudangrass, and these increases were in turn negatively correlated with wilt incidence and positively correlated with yields of both U.S. #1 tubers and tubers > 280 g. Additional benefits also included significant increases of tuber grade percentages for marketable tubers and of smooth tubers > 280 g. Benefits from sudangrass green manures beyond the effects of Verticillium suppression became further evident following a greenhouse study that involved field soil and sudangrass that had been grown in the same field. This study corroborated both field experiments by showing increased yields with green manures of sudangrass that approximated 5.5 t ha-1 dry wt. As with the field studies, these yield benefits also extended beyond the effects of Verticillium suppression and were closely associated with significant increases ofFusarium equiseti, F. oxysporum, andF. solani. Throughout all studies, sudangrass green manures significantly increased microbial activities with increased populations ofFusarium spp. and increased concentrations in soil of mineralizable N, organic P, K, Mn, along with the percent soil organic matter -all factors that could have contributed to significant increases of yield and quality.ResumenSe obtuvo información adicional sobre los efectos benéficos del sorgo para el incremento de rendimientos y calidad de papa Russet Burbank por medio de tres estudios. Dos de ellos mostraron un significativo incremento de U.S. #1 y tubérculos uniformes > 280g después de haber recibido sorgo como abono verde. Los efectos del sorgo (HS-33) no mostraron diferencias con el sorgo ...’brido (Tridan-8). Cuando se comparó el abono verde de sorgo con un tratamiento de barbecho, los resultados del primer estudio mostraron un promedio de incremento del rendimiento de 36% para tubérculos U.S. #1 > 280g y los del segundo estudio 34% para tubérculos U.S. #1. El mismo tratamiento de sorgo, superó a los abonos verdes de alverjilla, cebada y maíz dulce con rendimientos de U.S. #1 que variaron entre 27 y 61%. Junto con estas evidencias, los beneficios logrados fueron además un efecto de supresión de Verticillium. El N del suelo se incrementó significativamente después de un abonamiento verde con sorgo y este incremento estuvo negativamente correlacionado con la incidencia de marchitez y positivamente con el rendimiento tanto de U.S. #1 como de tubérculos > 280g. Los beneficios adicionales también incluyen un incremento significativo del porcentaje de tubérculos de grado comerciable y de tubérculos uniformes > 280g. Además de los efectos de supresión de Verticillium, los efectos del abono verde con sorgo se hicieron evidentes después de un estudio de invernadero que incluyó el uso de tierra de chacra y de sorgo que había crecido en el mismo suelo. Este estudio corroboró ambos expérimentes de campo, mostrando un incremento de rendimiento de aproximadamente 5.5 t ha-1 de peso seco con el uso de sorgo como abono verde. Como en el caso de los estudios de campo, estos beneficios en el rendimiento también se extendieron más allá de los efectos de supresión de Verticillium y estuvieron estrechamente asociados con un incremento significativo deFusarium equiseti, F. oxysporum yF. solani. A lo largo de todos los estudios, el uso de sorgo como abono verde incrementó significativamente las actividades microbianas, con un aumento en la población deFusarium spp. e incremento de las concentraciones de N mineralizable, P,K y Mn orgánicos, junto con el porcentaje de materia orgánica en el suelo, factores todos que podrían contribuir a un aumento de rendimiento y calidad.

Distribution of tobacco rattle virus and potato virus X in leaves, roots, and fruits and/or seeds of naturally-infected weeds

Weeds in tobacco rattle virus (TRV)-infested potato fields were examined for TRV and potato virus X (PVX) with the enzyme-linked immunosorbent assay. Questionable positive reactions were evaluated with immunosorbent electron microscopy. Of 615 weeds, representing 28 species, sampled over a two-year period, four species contained only TRV, three were infected only with PVX and eight had both viruses. Tobacco rattle virus was located only in the roots of five species and PVX was found only in the foliage of five species. Seeds and/or fruits of three species contained TRV while two contained PVX. Only one weed species,Solanum sara choides, contained both viruses in all plant portions tested. Potato virus X was not detected in weeds within a field planted with PVX-free potato seed.ResumenEn campos de papa infestados con tobacco rattle virus (TRV) las malezas fueron examinadas para TRV y el virus X de la papa con la técnica serológica con conjugado enzimático (ELISA). Reacciones positivas dudosas fueron evaluadas con Absorción inmunológica en Microscopía electrónica. De 615 malezas, representando a 28 especies, colectadas en un período de dos años, cuatro especies tuvieron solo TRV, tres se hallaron infectadas con PVX y ocho tuvieron ambos virus. TRV se localizó sólo en las raíces de 5 especies y PVX fue hallado sólo en el follaje de 5 especies. Semillas y/o frutos de 3 especies tuvieron TRV mientras que 2 tenían PVX. Sólo una especie de maleza,Solanum sarachoides tubo ambos virus en todas las partes de la planta. PVX no fue detectado en malezas dentro de un campo plantado con semilla de papa libre de PVX.