Effect of temperature and latent viruses on atypical ring rot symptoms of Russet Burbank potatoes

The ring rot bacterium,Corynebacterium sepedonicum (Spieck. and Kotth.) Skapt. and Burkh. [Clavibacter michiganense subsp.sepedonicum (Spieck et Kotth.) Davis et al.], and latent potato viruses (potato virus S and potato virus X) were investigated for their effect on atypical (ATYP) ring rot symptom development on Russet Burbank potato plants at different temperatures. Plants grown at 21 C from stem cuttings root-inoculated withC. sepedonicum developed typical wilting and chlorotic symptoms of ring rot that were equally severe on virus-free (VF) and virus-infected (VI) plants. All VF and VI plants grown at 15 C from inoculated stem cuttings exhibited ATYP symptoms that included extreme stunting, resetting, and chlorotic symptoms of ring rot. More severe ATYP symptoms developed on VI than on VF plants. Up to 5 wk after inoculation withC. sepedonicum, ATYP symptom severity ratings of both VF and VI plants increased and declined thereafter. The ATYP severity ratings were highly correlated with fresh weight of plants with high severity ratings being associated with low fresh weights. These results emphasize the need to determine the role of temperature and viral pathogens on ring rot symptomology in existing and newly developed potato cultivars and thereby enable better field detection of bacterial ring rot.     

Effect of the ring rot pathogen and latent potato viruses on ring rot symptoms and yield of potatoes

The ring rot bacterium,Corynebacterium sepedonicum (Spieck. and Kotth.) Skapt. and Burkh., and latent potato viruses (potato virus S and potato virus X) were investigated for their effect on ring rot symptom development on potato plants in the greenhouse and on symptom development and yield of potatoes in the field. Both virus-free (VF) and virus-infected (VI) Red Pontiac stem cuttings root-inoculated with ring rot bacteria in the greenhouse developed typical (T) ring rot symptoms, and symptom severity did not differ between VF and VI plants. In a field study, both VF and VI Russet Burbank seed pieces knife-inoculated with ring rot bacteria produced plants with atypical (A) and T ring rot symptoms as well as a combination of both types. The data suggest that more A than T symptoms develop on VI plants and more T than A symptoms develop on VF plants. Combined infection with the ring rot pathogen and the latent potato viruses resulted in greater yield losses of total and marketable Russet Burbank tubers than infection with the bacterial or viral pathogens alone.     

An hypothesis for selection of strains of potato leaf roll virus by passage through Physalis floridana

Symptomatically distinct isolates of potato leaf roll virus were transmitted from White Rose to Russet Burbank potato by aphids and by grafting, from White Rose potato toP. floridana by aphids, and fromP. floridana toP. floridana by aphids. Isolates from White Rose potato generally produced stable and characteristic secondary leaf roll symptoms (but not primary leaf roll symptoms) when transmitted to Russet Burbank potato but variable symptoms when transmitted toP. floridana. Isolates from two of the latter plants with moderate and severe symptoms generally incited stable and characteristic symptoms when transmitted to otherP. floridana plants. The stable symptoms produced by each of these isolates were not modified by infestingP. floridana plants with varying numbers of viruliferous aphids. The results obtained in this study corroborate previous evidence for the existence of strains of potato leaf roll virus. It is suggested that certain White Rose potato plants contained mixtures of leaf roll virus strains. Furthermore, it is postulated that these mixtures were at least partially separated by “natural” selection following transmission toP. floridana. This mechanism provides an explanation for the stable symptoms produced by isolates transmitted fromP. floridana toP. floridana.     

Long-Term survival ofCorynebacterium sepedonicum on contaminated surfaces and in infected potato stems

The survival of the ring rot bacterium,Corynebacterium sepedonicum, on contaminated surfaces and in infected stems was investigated by root inoculating potato stem cuttings with aqueous suspensions prepared from these materials. The pathogen survived for 24 mo on contaminated surfaces of burlap, kraft paper, and polyethylene plastic held at 12% relative humidity (RH) at either 5 or 20°C. It persisted for less than 14 mo on surfaces held at 94% RH at either temperature. Infectious ring rot bacteria were also recovered from dried, infected potato stems held for 26 mo in an unheated machine shed. These results emphasize the importance of strict sanitation and disinfestation procedures in maintaining potato seed stocks free of bacterial ring rot.     

Factors affecting ring rot development in root-inoculated potato plants originating from stem cuttings

Some of the factors that affected ring rot development in potato plants grown from stem cuttings and root-inoculated withCoryncbacterium sepedonicum were investigated. Isolates ofC. sepedonicum cultured and stored for a, year on agar media were as virulent as those that had been cultured for almost 5 months. Isolates cultured for periods over 2 years gradually lost their virulence; however, decline in virulence was not as rapid as had been previously reported. One isolate became more virulent by inoculating and recovering it from a susceptible potato plant. Ring rot symptoms developed more rapidly in the cultivar Red Pontiac than in the cultivar Netted Gem; however, disease severity eventually reached the same level in both cultivars. The more mature the plants were when inoculated, the greater was the rate of ring rot development. Duration of exposure of wounded roots to inoculum of the pathogen did not affect disease development. No ring rot bacteria were recovered from plants originating from apical cuttings of ring-rot-infected potato plants that exhibited partial wilting. By this technique, plants infected withC. sepedonicum were freed from this pathogen quickly and effectively.     

Freeing Russet Burbank potato plants from ring rot by stem cutting and tuber propagation

Apical stem cuttings removed from potato plants (cv. Russet Burbank) infected withCorynebacterium sepedonicum and expressing mild symptoms of bacterial ring rot were demonstrated to be free from the pathogen. This material remained free of ring rot through two additional stem cutting generations and when grown in the field for four successive tuber generations.     

Evaluation of immunofluorescence with monoclonal antibodies for detecting latent bacterial ring rot infections

Corynebacterium sepedonicum was detected in symptomless potato stems and tubers with immunofluorescence using monoclonal antibodies specific for the bacterial ring rot pathogen. The concentration of bacterial cells in potato tissue preparations ranged from >500 cells/microscope field to 1 cell per preparation. Symptomless tubers containing ring rot bacteria planted in field plots yielded plants with ring rot symptoms, plants with latent ring rot infections, or plants with no detectable levels of ring rot bacteria. Tubers with the greatest number of bacteria were most likely to develop plants expressing ring rot symptoms, but even some seed tubers with a low number of bacteria developed into plants with symptoms. Some seed tubers with high levels of ring rot bacteria produced plants with only low numbers ofC. sepedonicum.     

The effect of metribuzin interaction with potato viruses X and Y on potato foliage,yield and grade

Foliar treatment of potato (Solanum tuberosum L.) with metribuzin at 0.57–1.0 lb/A caused a necrotic reaction in leaflets of plants infected with potato virus Y (PVY), but not in plants infected with potato virus X (PVX) or potato leafroll virus. Necrosis symptoms resulting from metribuzin-PVY interaction were distinct from symptoms of either PVY infection or of metribuzin injury. This reaction was similar in the Russet Burbank, Lemhi Russet, and Pioneer cultivars. Russet Burbank infected with PVY and PVX, alone or in combination, was treated with metribuzin to study herbicidevirus interaction effects on yield. Secondary PVY infection alone caused a 57% yield reduction, and when combined with PVX caused a 71% yield reduction. Although leaflet necrosis was induced by the metribuzin-PVY combination, there was no significant yield interaction. Results suggest that post-emergence application of metribuzin can be used as an aid for detecting and removing potato virus Y infected plants from potato seed fields     

The latex agglutination test as a rapid serological assay forCorynebacterium sepedonicum

The latex agglutination test was evaluated for detection of the potato bacterial ring rot pathogen,Corynebacterium sepedonicum. The bacterium was detected in infected potato stems and tubers tested and in inoculated eggplant stems. Test reliability was confirmed using blind tests. A minimum of 10⁶ bacterial cells/ml was requisite for observable agglutination. Nonspecific reactions were not observed from healthy extracts of plant tissues. Nonspecific reactions with other bacteria maintained in pure culture were eliminated by addition of bovine serum albumin to sensitized latex preparations.     

Current status and future prospects of bacterial ring rot testing

The bacterial ring rot disease of potato (Corynebacterium sepedonicum) can be detected in seed potato lots by serological tests with greater accuracy than by visual field inspections. Indexing tests can make use of highly specific immunofiuorescence probes, enzyme-linked immunosorbent assays, and perhaps other procedures. Sensitivity and specificity of these procedures need to be determined in order to estimate the confidence with which ring rot can be detected in a seed lot. In addition to the laboratory tests, the sampling strategy determines the efficacy and sensitivity of the indexing procedure. Samples might consist of stems, leaf petioles, or tubers in single or composite units. Disease incidence and number of plants sampled also determine the confidence level with which ring rot can be detected in a potato seed lot. Although research has been conducted on many aspects of ring rot testing procedures, further work needs to be done. Nevertheless, it is anticipated that indexing potato seed lots for the presence of ring rot will be a significant factor in control and eradication of the disease.     

Survival ofCorynebacterium sepedonicum in potato stems and on surfaces held at freezing and above-freezing temperatures

The survival ofCorynebacterium sepedonicum, the bacterial ring rot pathogen, in infected potato stems and on burlap surfaces held at various freezing and above-freezing temperatures was investigated by root-inoculating potato stem cuttings with aqueous suspensions prepared from these materials. Infectious bacteria were recovered from dried Russet Burbank stems held for 44 mo in an unheated machine shed and from dried Warba stems held for 55 mo. Inoculum from dried stems of all cultivars held for 63 mo did not incite symptoms; however, inoculum from Russet Burbank stems incited symptomless infection in 10% of the inoculated plants. This 63-mo survival period exceeds a 26-mo survival period previously reported. Ring rot bacteria survived and remained infectious for at least 18 mo on burlap surfaces subjected to temperatures of ?40° to ?5°C, alternating temperatures of -5° to 5°C, or a constant temperature of 5°C. Inoculum from burlap stored at the lower temperatures caused the most severe symptoms. These results stress the need for keeping crop debris away from potato operations and for using proper decontamination procedures to maintain potato seed stocks free of ring rot.     

Potato Ring Rot in Norway: Occurrence and Control

Potato ring rot, caused by the bacterium Clavibacter michiganensis subspecies sepedonicus, is considered to be one of the internationally most important seed potato diseases (Smith et al.; Eur J Plant Pathol 107:739–748, 2001) and has been a problem in Norwegian potato production since its first detection in 1964. Since 1965, Norway has had its own national legislation for the control of the disease. In recent years, this legislation has evolved to be more similar to the EU Commission Directive 2006/56/EC. In 1999, the Norwegian Food Safety Authority initiated an eradication program for potato ring rot with the aim of selling potatoes to other European countries. During the project period (1999–2008), efficient systems for sampling, analysis and eradication measures were built. From 1999 to 2002, the occurrence of potato ring rot in commercial potato production was monitored in all counties. Sampling was carried out according to the instructions of the Norwegian Food Safety Authority, while testing of samples was (from 2000 onwards) carried out by Bioforsk laboratories with modern serological and molecular detection methods. When ring rot was detected in a potato lot, the grower had to implement strict eradication measures. The survey was followed up with two monitoring periods, 2003–2004 and 2005–2008. During the project period, 328 cases of potato ring rot were found. The counties Hedmark, Nordland, Troms, and Tr?ndelag accounted for most of these. The main objectives of this study were to describe the occurrence of potato ring rot in Norwegian potato production and to evaluate the effectiveness of the eradication measures employed for the control of the disease. This survey showed that the overall ring rot situation did improve considerably during the project period (1999–2008), both in relation to prior periods, and when comparing the surveying and monitoring periods. Problem areas where monitoring must be continued remain.     

Symptoms induced by Andean potato latent virus in wild and cultivated potatoes

Summary The symptomatology of Andean potato latent virus (APLV) was studied in several wild potato species and potato cultivars using isolates Caj, Hu and Ay from Peru. In greenhouse tests, the virus was latent in most isolate/cultivar combinations with primary infection but secondary infection commonly caused symptoms. Wild species infected with the different isolates normally reacted with symptoms with either type of infection. The main symptoms were mosaics, chlorotic netting of minor leaf veins and, with wild species, leaf deformation; the netting symptom was typical only with Caj. In infected cultivars growing in the field, an additional symptom, rugosity, sometimes also developed and environmental conditions at high altitude seemed to enhance symptom formation. Very severe symptoms were found in a cultivar jointly infected with APLV and Andean potato mottle virus. Transmission of APLV from an infected plant to its tubers was erratic.     

马铃薯环腐病菌快速检测方法(NCM-ELISA)的建立

建立检测马铃薯环腐病菌NCM-ELISA方法并组装成试剂盒,应用于检测、检疫和流行病学调查具有实践意义。本研究以马铃薯环腐病菌为抗原,制备兔抗血清,利用碱性磷酸酯酶标记的羊抗兔血清(GAR-AP)为酶标二抗,建立了马铃薯环腐病菌NCM-ELISA快速检测方法。结果表明:抗血清的最佳工作浓度为1:400,最低检出菌液浓度为1.0×106个.mL-1,特异性也比较强。因此,该方法具有敏感性高、特异性强、速度快、实用方便等特点,可以应用于马铃薯环腐病菌的快速检测和诊断。     

Purification of potato leaf roll virus and an evaluation of methods for its diagnosis

To evaluate four diagnostic methods for potato leaf roll virus (PLRV), an antiserum was prepared against a virus preparation purified from infectedDatura stramonium L. by an exudation method. The antiserum had a titer of 1:64 in microprecipitin tests. In a procedure developed subsequently PLRV was purified by a method that involved grinding liquid nitrogen frozen stems, petioles, and veins from different solanaceous hosts. A chloroform and n-butanol clarification was done followed by two cycles of differential centrifugation. On sucrose gradients, these preparations formed one band containing spherical particles 25 nm in diameter. In Ouchterlony double-diffusion plates, the antiserum reacted positively with virus preparations from frozenPhysalis, Datura or potato tissue partially purified by two cycles of differential centrifugation. No visible reaction was obtained between the antiserum and the virus preparation from density gradient centrifugation. Antiserum neutralized infectivity of 40–50% of the virions in a partially purified preparation. No virus peak was detected in the scanning patterns obtained after a mixture of antiserum and virus was centrifuged on a sucrose density gradient. A few virus particles were seen attached to serologically specific grids. Methods to diagnose PLRV in infected potato tubers were then compared. In the first, aphids were used to acquire the virus from tuber sprouts. They transmitted the virus to 100% of thePhysalis test plants. Results of the second method, visual inspection of symptoms on potato plants, were similar to those of the first method. Sarkar’s electron microscopic method and immuno-specific grids were less efficient than aphid transmission to diagnose PLRV in tuber sprouts. The low virus concentration in infected tissue made these last two methods unreliable.     

Elimination of viruses and hypersensitivity to potato virus Y (PVYo) in an important sudanese potato stock (Zalinge)

Viruses that infect naturally an important Sudanese potato stock Zalinge were detected using enzyme-linked immunosorbent assay, immunosorbent electron microscopy and sap-inoculation to test plants. All of the 19 plants of Zalinge tested were infected with potato leaf roll virus (PLRV) and potato virus S (P VS), and five plants also with potato virus X (PVX). No potato virus Y (PVY), A (PVA) nor M (PVM) were found. The viruses were eradicated with thermo and chemotherapy using standard procedures. The combination of both therapies did not result in any virus-free plants, but resulted in poor plant survival. Thermotherapy reduced the incidence of PLRV and PVS by 45% and 50%, respectively, and one virus-free plant was obtained. It grew vigorously in the greenhouse, was symptomless and had a significantly increased tuber yield compared to the virus-infected plants. Following sap-inoculation with PVY^O, Zalinge showed mosaic symptoms, developed necrosis in the leaves and stem and died 14 days post-inoculation. However, the plants of Zalinge infected with PVY^N remained symptomless, which suggested that hypersensitivity was specific to PVY^O. The fast development of lethal necrosis following infection with PVY^O may contribute to the low incidence of PVY in Zalinge in the field in Sudan.     

Extraction ofclaviba cter michiganensis subsp.sepedonicus from composite samples of potato tubers

The presence ofClavibacter michiganensis subsp.sepedonicus was detected by immunofluorescence and ELISA in diluent in which cores from 200 potato tubers had been incubated on a rotary shaker. By this procedure the ring rot pathogen was detected in composite samples from naturally infected tubers and tuber samples “spiked” with infected tissue or a pure culture of the pathogen. Populations of saprophytic bacteria increased about 100-fold in the diluent during 18 h of incubation but did not interfere with serological detection of C.m. sepedonicus. Some of the results suggest thatC. m. sepedonicus cells multiply during incubation of tuber samples. Extraction of ring rot bacteria from potato tuber tissue by incubation on a rotary shaker requires little work and minimizes the amount of plant tissue in the extract compared to the standard extraction procedure involving maceration and differential centrifugation.     

AC Ptarmigan: An early maturing potato cultivar with good chipping and fresh market quality

AC Ptarmigan is an early maturing, buff skin, cream flesh potato cultivar which has good, stable chip quality and can be processed directly from the field. The cultivar has uniform attractive tubers with shallow eyes. It is moderately resistant to common scab, early blight, potato virus Y and potato leafroll virus. It is susceptible to late blight and shows clear field symptoms when infected with bacterial ring rot.     

Persistence ofCorynebacterium sepedonicum in soil and in buried potato stems

The effect of moisture content and temperature on the persistence, in soil, of cells of the ring rot bacterium,Corynebacterium sepedonicum (Spieck. and Kotth.) Skapt. and Burkh., was followed with root-inoculated, rooted potato stem cuttings. Ring rot bacteria were still viable after 284 days in a sterilized Lethbridge silt loam moistened to field capacity and incubated at 15°C. However, the cells did not survive beyond 6 days in two non-sterile silt loams at field capacity and 20°C. In non-sterile Lethbridge silt loam, persistence of the pathogen increased as soil moisture content and temperature decreased. Cells persisted for 10 and 15 days, respectively, in soil at 50% field capacity held at 15 and 10°C. Ring rot bacteria were not recovered after 88 days from a non-sterile Lethbridge silt loam moistened to the wilting point and held at a temperature fluctuating between 10 and 20°C, or from soil at field capacity and at a temperature fluctuating between ?5 and +5°C. They survived for 362 days in soil at the wilting point at mean temperatures of 0 or ?10°C, but were not viable after 278 days in soil at field capacity and a mean temperature of ?10°C. In excised, infected potato stems held in a non-sterile Lethbridge silt loam, the pathogen persisted for 325 days in soil at the wilting point and a mean temperature of 0°C. These results suggest that soil infested with ring rot bacteria should be kept well moistened during warm periods to inactivate these bacteria and to ensure that they do not contaminate healthy tubers that may be stored or grown there later.