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.     

Application of a PCR-based test for detection of potato late blight and pink rot in tubers

A polymerase chain reaction (PCR)-based test for potato late blight (Phytophthora infestans) and pink rot (P.erythroseptica, P. nicotianae) diseases has been developed for use with potato tuber tissue. Primers based on sequence analysis of the ITS2 region of ribosomal DNA of late blight and pink rot pathogens were utilized in PCR assays of inoculated tubers and tubers harvested from plots known to have late blight and/or pink rot. Assays of artificially inoculated Kennebec and Russet Burbank tubers revealed thatP. infestans was detected by PCR as early as 72 h after inoculation and in the absence of visible symptoms. Much higher detection frequencies were obtained by PCR compared with plating on selective medium or placement of tissue in moist chambers. Tubers from plots known to have late blight and/or pink rot were tested using the PCR assay. Assay of late blight lesions showed ca. 80% recovery for late blight-infected tubers from the field. Results indicate that the PCR assay provides a rapid and accurate test for diagnosis of late blight and pink rot in potato tubers.     

Leak syndrome of potato in Tunisia caused byPythium aphanidermatum andPythium ultimum

Summary TwoPythium spp. were isolated from diseased tubers exhibiting rots at harvest, in summer stores and also in refrigerated storage. Symptoms shared features described for both pink rot caused byPhytophthora erythroseptica and leak caused byPythium spp. The causal agents were identified asPythium aphanidermatum andP. ultimum by morphological and physiological observations and by fingerprinting using oomycete specific primers to amplify the internal transcribed spacer (ITS1) within ribosomal DNAs. The optimum temperatures for infection were 30°C forP. aphanidermatum and 25°C forP. ultimum, corresponding to the optimum temperatures for growth in vitro. The optimum concentration for infection of tubers inoculated by dipping in a suspension of oospores or hyphal swellings after wounding was found to be 10³ reproductive organs/ml, whereas the infection threshold was 10 reproductive organs/ml.     

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.     

Resistance of tubers from different potato cultivars to soft rot caused byErwinia carotovora subsp.atroseptica

Mechanically harvested tubers of 14 potato cultivars grown on both loamy sand and silt loam soils were evaluated for resistance to bacterial soft rot caused byErwinia carotovora subsp.atroseptica. Cultivars were also assayed for calcium and dry matter content to determine possible correlations with soft rot resistance. Resistance of potato tubers to bacterial soft rot was assayed after harvest by inoculating tubers and determining percent surface area decayed after four days in a mist chamber. Tubers of the cultivars differed widely in resistance to bacterial soft rot. The ranking of the resistance of tubers from different cultivars to bacterial soft rot was similar for both soils, although disease severity in tubers from a particular soil type varied with the season. Of the cultivars tested, tubers of Butte, Russet Burbank, and Nor-gold Russet were ranked as the most resistant, whereas tubers of Redsen, Norchip, Norland and Belchip were rated as the most susceptible. Tubers of Rhinered, Red La Soda, Superior, Pontiac, Atlantic, and Nooksack were intermediate in resistance. Neither calcium concentration in medullar tissues nor dry matter of potato tubers alone could be correlated with ranking of the cultivars with respect to severity of bacterial soft rot. However, a multiple linear regression model incorporating both variables indicated that tubers with a high content of both calcium and dry matter were likely to be less susceptible to bacterial soft rot than were tubers with lower percentages of these variables.     

Resistencia de tuberculos a las fusaria que afectan papa en el Peru

Fungi of the genusFusarium Link isolated in Perú from potatoes (Solanum tuberosum L. subsp.andigena Juz. & Buk.) affected by: i) wilt, ii) dry rot of stored tubers, iii) secondary rot in tubers affected by “cork” disease (potato mop-top virus?), caused dry rot when inoculated to tubers of Renaacimiento variety. The identification of some of theseFusaria suggests thatFusarium solani Snyder & Hansen is associated with wilt and dry rot, andFusarium oxysporum Snyder & Hansen with rot secondary to cork disease. Tubers of eight potato varieties inoculated with fourFusaria representative of those isolated showed a great range in levels of susceptibility to colonization by theseFusaria, Sapa being the most susceptible variety, and Mantaro appearing to be the most resistant. These results suggest that useful levels of resistance toFusarium tuber rot are available in the Peruvian germ-plasm.     

An agglutination test for the serodiagnosis ofCorynebacterium sepedonicum

Antisera specific forCorynebacterium sepedonicum were produced in three rabbits and in a goat. Bacterial cell agglutination titers of 640, 1280, and 1280 were recorded for the rabbit sera and 320 for the goat antiserum. All antisera reacted equally well with twelve isolates ofC. sepedonicum obtained from Canada, California, Montana, Oregon, Washington, and Wisconsin. No cross-reactivity was observed when the anti-C. sepedonicum sera were tested against five otherCorynebacterium spp.and seven other species of plant pathogenic bacteria. Using the antisera collected from rabbits, an effective and reliable agglutination test was developed for the detection ofC. sepedonicum in potato stem and tuber tissue. Extracts from tubers affected by other maladies incudingErwinia spp. (soft rot),Fusarium spp. (dry rot),Phytopthora erythroseptica (waterrot),and Pythium debaryanum (leak) or tubers otherwise free fromC. sepedonicum infection did not produce an agglutination reaction when tested with anti-C. sepedonicum serum.     

Detection ofCorynebacterium sepedonicum in potato cultivars with different propensities to express ring rot symptoms

Various potato cultivars were grown in field plots from seed pieces inoculated withCoryneacterium sepedanicum by vacuum infiltration. Foliage symptoms were recorded during the growing season and tuber symptoms at harvest. Cultivars were ranked according to the frequency with which the progeny tubers expressed external bacterial ring rot symptoms. Those that yielded 50–100% symptomatic tubers were placed in symptom expression class (SEC) 1; those that produced 25–49%, 10–24%, and ≤9% symptomatic tubers were placed, respectively, in SEC 2,3, and 4. The incidence of latent ring rot infections in stems and tubers were similar among cultivars in the different SEC classes. Bacterial population densities, quantified by immunofluorescence, were as high as 10¹⁰ cells/g in stems from cultivars of all SEC classes. Mean populations in tubers ranged from 10⁶ – 10⁷ cells/g and did not differ significantly among cultivars.     

Genetic Diversity of Pathogenic <Emphasis Type="Italic">Fusarium semitectum</Emphasis> Isolates from Potato Tubers,Using PCR-IGS-RFLP Markers

Fusarium semitectum is one of the important causal agents of dry rot of potato tubers in the world. In order to determine genetic variability among 41 isolates of F. semitectum, morphological and molecular studies were carried out. All F. semitectum isolates were recovered from infected potato tubers with dry rot symptoms collected from four provinces in Iran. According to macroscopic and microscopic characteristics, 41 isolates of F. semitectum were classified in two morphotypes (morphotypes I and II). All 41 isolates were evaluated for their pathogenicity on healthy potato tubers. Tuber rot symptoms were observed on the 21st day after inoculation of Fusarium isolates on the tubers tested. The measurement was done by comparing the depth and width of lesion expansion among the isolates. Molecular characterization through PCR-IGS-RFLP analysis by six restriction enzymes (AluI, BsuRI, Eco88I, MspI, TaqI and PstI) divided the 41 isolates of F. semitectum into two separated clusters that were in accordance with the morphological characterization.     

Ring rot symptom development on potato cultivars and lines in southern Alberta

Summary Plants were grown in the field from seed pieces of potato cultivars injected with ring rot bacteria (Corynebacterium sepedonicum). Symptoms were produced with both 18 and 180 colony forming units (cfu) on cvs Norchip and Red Pontiac and with 180 cfu on cv. Belrus plants. Tuber symptoms were detected in all cultivars except Belrus and Teton. Tuber progeny produced plants that developed top symptoms on all cultivars except those of cv. Nooksack, Russet Burbank, and Teton. Tuber progeny of the second crop produced both plants and tubers with symptoms developing only in the cv. Nooksack. In another 3-year experiment, variability in the disease response of selected cultivars and lines was examined following knife-inoculation of tuber seed with a high level of ring rot bacteria. Significant correlations between top and tuber symptoms were detected, but they were not high enough to make unnecessary the examination of both top and tuber symptoms in ring rot disease selection studies. Contribution no. 3879111     

Detection and identification of fluorescent compounds in potato tuber tissue with corky patch syndrome

A corky patch syndrome that effects potato tuber tissue may be a later manifestation of pink eye disease of potato although an actual cause and effect relationship between the two diseases has not been firmly established. The causal agent for pink eye of potato is unknown but the disease has been associated with the fungiVerticillium andRhizoctonia and the bacteriumPseudomonas fluorescens. Pink eye and corky patch symptoms on the periderm of affected tubers are accompanied by a band of tissue beneath that is intensely auto-fluorescent when viewed under ultraviolet illumination. Studies to determine the cause of the fluorescent reaction were performed using HPLC and a fluorescence monitor. Three phenylpropanoid compounds, chlorogenic acid, esculin and scopoletin, were found to be involved. It appears that these compounds are produced by tuber tissues in response to pathogen invasion and also as part of the wound healing process. Tissues with corky patch syndrome, silver scurf and root-knot nematode contained high concentrations of chlorogenic acid and esculin and low concentrations of scopoletin. Tissues infected with dry rot were visibly less fluorescent, and contained less chlorogenic acid and esculin, and no detectable level of scopoletin.     

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.     

Bacterial soft rot potential in washed potato tubers in relation to temperatures of tubers and water during simulated commercial handling practices

The bacterial soft rot potential in potato tubers was affected by differences in temperature between tubers and suspensions ofErwinia carotovora at the time of inoculation by immersion. In general, disease severity after incubation was higher when tuber temperatures were higher as opposed to equal to or lower than that of water containing cells of the bacterium. Disease severity was also greater when tubers were stored at 20° to 23°C in contrast to 4° or 26° to 30°C for 16–18 h prior to immersion. Tubers with a pulp temperature of 8°C were more prone to bruise injury as compared with those at 18°C when struck with a pendulum type bruising instrument. When the injured tubers were inoculated and incubated, most bruises became infected with soft rot bacteria.     

Differences in tuber rot development for North American clones ofPhytophthora infestans

The relative aggressiveness ofPhytophthora infestons clones in potato tubers was compared in three trials using 7 to 24 isolates of 2 to 4 clones. Visible rot developed slowly at 13C with isolates of the US-1 genotype, the only significant clone found in North America prior to 1979, but substantially faster with most isolates of the newer clonal genotypes US-6, US-7 and US-8. Certain US-7 isolates were similar to US-1, and US-6 isolates also had a broad range of aggressiveness. Secondary infection byFusarium sp. increased rot development in many instances, but this effect was not clone-related. Differences in rot development may affect potato storage or late blight disease transmission.     

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.     

Recovery ofVerticillium dahliae from North American certified seed potatoes and characterization of strains by vegetative compatibility and aggressiveness

Samples of tubers collected from commercial potato seed lots produced across North America were assayed forVerticillium dahliae. V. dahliae was successfully isolated from 65 of 224 seed lots tested, a successful isolation rate of nearly 30%. Vegetative compatibility of the isolates was assessed through complementation tests using nitrate non-utilizing mutants. AllV. dahliae isolates belonged to vegetative compatibility group (VCG) 4. Of the 162 isolates recovered, 64% belonged to VCG 4A, 33% to VCG 4B, and 3% to VCG 4AB. All 39 of the isolates tested in the greenhouse on potato cv. Superior were pathogenic to potato. Disease symptoms developed earlier, were more severe, and plants died earlier when inoculated with VCG 4A compared to 4B isolates. As a group, AUSPC values were significantly higher (p=0.05) for VCG 4A than for 4B isolates. These data suggest that (1) commercial certified seed tubers from diverse locations are commonly infected withV. dahliae and thus may serve as primary sources of the pathogen; (2) potato isolates ofV. dahliae in North America belong to VCG 4A and 4B and these strains are widely distributed via seed tubers; and (3) VCG 4A and 4B are distinct pathotypes ofV. dahliae that vary in their aggressiveness to potato.     

Variation in pathogenicity on potato tubers and sensitivity to thiabendazole of the dry rot fungusFusarium avenaceum

Summary The majority of isolates ofFusarium avenaceum caused dry rot on potato tubers; many were as pathogenic asF. coeruleum. Pathogenicity ofF. avenaceum was not related to the plant species from which the isolates originated. Tubers of potato cv. Cara were more susceptible than those of cvs Romano or Maris Piper. Temperature (5–15° C) had no effect on lesion depth but lesions tended to be slightly wider at the lowest temperature. Two isolates (of 61) from wheat and white lupin had a moderate level of resistance to thiabendazole. The results are discussed in relation to the control of dry rot in stored potato tubers.     

Expression of the chicken lysozyme gene in potato enhances resistance to infection byErwinia carotovora subsp.atroseptica

Infection of potato plants and tubers with the bacteriumErwinia carotovora subsp.atroseptica produces blackleg and soft rot diseases, which cause significant losses to crops and stored potatoes. In order to obtain resistance against this bacterium, the genechly encoding the enzyme lysozyme from chicken was introduced into potato plants (cv. Desirée) viaAgrobacterium- mediated transformation. Sixty-three and 69 transgenic potato clones were evaluated in the greenhouse for resistance to blackleg and soft rot diseases, respectively. Results reported in this paper indicate that 21%-29% of the potato clones showed increased resistance to infection by the bacteriumE. c. subsp.atroseptica T7, as revealed by a reduced severity of blackleg or soft rot symptoms. Nine clones showing different levels of resistance were selected for further molecular analysis. The number of copies of the transgene integrated in the plant genome of these clones was estimated by Southern blot analysis. The level of transgene expression, detected by Northern blot analysis, correlated with the level of resistance detected in these clones.     

Quaggy Joe: A high-yielding, round, white potato variety for fresh market

The Quaggy Joe potato variety is high-yielding and medium to medium-late maturing with attractive, round-oval, white-skinned, white-fleshed tubers with medium-shallow pink eyes. Its major use is expected to be as a maincrop tablestock variety. Quaggy Joe is resistant to the potato leafroll virus, and is also moderately resistant to early blight (Alternaria solani), dry rot (Fusarium sambucinum), and soft rot (Erwinia carotovora subsp.carotovora). Quaggy Joe tubers have shown very little shatter or blackspot bruising, but sprout earlier than Atlantic. Young plants have shown sensitivity to the herbicide metribuzin.