GROWTH,TUBER FORMATION AND SPREAD OF CYPERUS ROTUNDUS L. FROM SINGLE TUBERS*

Summary. Single tubers of Cyperus rotundus L. were planted at intervals over the year. Plant growth was slow and sprouting of tubers was inhibited at temperatures below 20°C, but tubers overwintered at temperatures above freezing point. In the warm season, plant growth and tuber formation rate closely followed air temperature and tubers were forming within 1 month from planting. No inflorescence appeared during the cool season. In autumn-planted C. rotundus grown in containers, the ratio of aerial to subterranean weight decreased from 1·1 in December to 0·2–0·4 in summer. The weight of tubers in mid-summer was about 10 times more than that present in December. Tubers formed at ail times of year and at various locations on plants sprouted readily in laboratory tests (76–100% sprouting). C. rotundus planted in March at wide spacings was grown in field conditions free of other plant competition for 20 months. Within 2 months the plants had spread to 90 cm. At the end of the first and the second summer of growth, the mean area of one plant was 7·6 m² and 56·7 m², respectively, and patches had expanded then by 2·8 m and 5·4 m, respectively, from the initial shoot. After 20 months of growth all tubers were present within the 0–40 cm soil depth, 60–70% of them in the 0–20 cm layer. About 30% of the tubers were within 1 m and 60% within 2 m of the plant centre. Under the patch centre there were about 1000 tubers per m² with 0·3 kg dry weight; in the upper 20 cm more than 3500 tubers weighing 0·9 kg were present per m³ of soil. Croissance, formation de tubercules et propagation de Cyperus rotundus L. issu de tubercules uniques     

EFFECT OF MINIMUM SOIL TEMPERATURE ON DIFFERENTIAL DISTRIBUTION OF CYPERUS ROTUNDUS AND C. ESCULENTUS IN THE UNITED STATES*

Summary. The response of tubers to low temperatures was investigated to gain insight into a physiological basis for the differential distribution of Cyperus esculentus L. (yellow nutsedge) and C. rotundus L. (purple nutsedge) in the United States. Only C. esculentus tubers survived the winter of 1968–69 in the field at Urbana, Illinois. Less than 10% of C. rotundus tubers survived at 2°C for 12 weeks, whereas more than 95% of C. esculentus tubers survived this treatment. Exposures to -2°C for 4 h or longer killed 50% of C. rotundus tubers, whereas - 6·5°C was required to kill 50% of C esculentus tubers. C. rotundus distribution is restricted to regions where the soil seldom freezes, whereas C. esculentus is distributed in regions where the soil temperatures often get below freezing. Survival of C. esculentus tubers in soil which frequently freezes may account for its wide distribution. Death of C. rotundus tubers in soils which freeze apparently is the reason why the species is restricted to the southeastern and southwestern regions of the U.S.A. L'Influence de la température du sol sur la répartition différentielle de Cyperus rotundus et de Cyperus esculentus aux Etats-Unis     

Tuber transmission of ‘Candidatus Liberibacter solanacearum’ and its association with zebra chip on potato in New Zealand

Zebra chip, an emerging disease of potatoes, has recently been associated with ‘Candidatus Liberibacter solanacearum’ in New Zealand. The phloem-limited bacterium is known to be vectored by the tomato potato psyllid (Bactericera cockerelli). In this study, the role of tuber transmission in the spread of Ca. L. solanacearum was investigated by re-planting potato tubers infected with Ca. L. solanacearum in the absence of the psyllid. Nested PCR demonstrated that Ca. L. solanacearum could be transmitted from the mother tubers both to the foliage of growing plants and to progeny tubers, resulting in symptomatic and asymptomatic plants. Of 62 Ca. L. solanacearum-infected tubers four did not sprout symptomatic of zebra chip. A further two plants developed foliar symptoms associated with zebra chip during the growing season and died prematurely. Fifty-six of the infected tubers produced asymptomatic plants, although Ca. L. solanacearum was detected in the foliage of 39 of them indicative of transmission into asymptomatic progeny plants. At harvest, Ca. L. solanacearum was found in the daughter tubers of only five of the 39 asymptomatic plants, and only one of these plants was found to have zebra chip symptoms in the daughter tubers. Our results show that tuber transmission of Ca. L. solanacearum could play a role in the life cycle of this pathogen, providing a source for acquisition by Bactericera cockerelli and for movement of the pathogen to other regions of New Zealand via transport of seed tubers.     

Field Observations on Blackleg in England1

Inoculation of seed tubers with Erwinia carotnvora (Jones) Bergey et al. var. atroseptica (van Hall) Dye before planting resulted in early death (especially with sprouted seed), blackleg stems and decreased yields. Apical inoculations had most, and stolon inoculations the least, effect on growth and yield. Even plants without blackleg symptoms were more stunted and had fewer stems than plants from uninoculated seed. Rotting of seed tubers often stopped in dry weather and started again later, probably caused, or assisted by, insects breaching the wound barrier. Many other organisms can also rot seed tubers including Phytophthora erythroseptica Pethybridge (pink rot), Fusarium spp. (dry rot), Verticillium spp. (wilts) and Rhizoctonia spp. (black scurf). The bacteria have been shown to spread along rows underground and to different stocks within the same field, presumably in air, but season to season spread by the potato digger has not been demonstrated.     

Experiments with Cyperus rotundus L. II. Effects of some herbicides and growth regulators

Soil-incorporated butylate, EPTC and vernolate had only small effects on nutgrass (Cyperus rotundus L.) shoot numbers and the germination of recovered tubers. MSMA, 2,4-D, glyphosate and cyperquat all killed top growth and reduced the germination of recovered tubers in both field and pot trials. Naptalam increased shoot number and tuber production. Foliar sprays of abscisic acid, chlorflurenoi and CCDP (3-carboxy-1-(p-chlorophenyl)-4,6-dimethyl-2-pyridone) had little or no effect. Ethephon slightly increased the number of attached tubers with shoots, but NIA 10637 (.ethyl hydrogen-1-propylphosphonate) had inconsistent efl'ects. MH inhibited tuber bud germination, TIBA increased shoot numbers slightly, and daminozide reduced tuber production and the germination of detached tubers. None of the growth regulators tested appears potentially useful for nutgrass control. Expériences avec le Cyperus rotundus L. II. Action de quelques herbicides et substances de croissance Le butylate, l'EPTC et le vernolate incorporés au sol n'ont eu que peu d'efficacité contre le cyperus (Cyperus rotundus L.) en ce qui concerne le nombre de pousses et la germination des tubercules récoltés. Le MSMA, le 2,4-D, le glyphosate et le cyperquat ont tous détruit la zone terminale de croissance et réduit significativement la germination des tubercules récoltés dans les essais, soit au champ, soit en pots. Le naptalame a augmenté le nombre de pousses et la production de tubercules. Des pulvérisations sur les feuilles d'acide abscissique, de chlorflurénol et de CCDP (3-carbo.xy-1-(p-chlorophényl)-4,6-diméthyl-2-pyridone) n'a eu que peu ou pas d'effets. L'ethéphon a légérement accru le nombre de tubercuies fixés aux racines, mais le NIA 10637 (hydrogéne-1-propylphosphonate d'éthyle) n'a eu que des effets incohérents. L'hydrazide maléique a inhibé la germination du bourgeon du bulbe, le TIBA a accru légérement le nombre de pousses, et le daminozide a réduit la production des tubercules et la germination des tubercules détachés. Aucune des substance de croissance essayées n'apparait potentiellement utilisable pour la lutte contre le cyperus. Versuche mit Cyperus rotundus L. II. Wirkung einiger Herbizide und Wachstumsregulatoren In den Boden eingearbejtetes Butylat, EPTC und Vernolat hatte nur eine geringe Wirkung auf die Anzahl der Sprosse und den Austrieb der Knollen von Cyperus rotundus L. MSMA, 2,4-D, Glyphosate und Cyperquat toteten die oberirdischen Pflanzenteile ab und verringerten den Austrieb der Knollen in Feld- als auch in Gefässversuchen. Naptalam bewirkte eine Zunahme der Sprosszahl und erhöhte die Knollenbildung. Blattspritzungen mit Abscisinsäure, Chlorflurenoi und CCDP (3-Carboxy-1-(p-chlorphenyl)-4,6-di-methyl-2-pyridon) hatten eine geringe oder gar keine Wirkung. Durch Ethephon nahm die Anzahl der Knollen mit Sprossen zu, NIA 10637 (Äthyl hydrogen-1-propylphospho-nat) hingegen zeigte widersprüchliche Wirkungen. MH hemmte den Austrieb der KnoUenknospen, TIBA förderte leicht die Zahl der Sprosse und Daminozid verringerte die Knollenbildung und den Austrieb abgetrennter Knollen. Von den gepruften Wachstumsregulatoren scheint keiner fur die Bekampfung von Cyperus rotundus geeignet zu sein.     

The MeloTuber Test: a real‐time TaqMan® PCR‐based assay to detect the root‐knot nematodes Meloidogyne chitwoodi and M. fallax directly in potato tubers

Potato is one of the many important hosts for the root‐knot nematodes Meloidogyne chitwoodi and M. fallax that can infest roots as well as tubers. In the latter they may cause surface galls and necrotic spots below the skin. In the EU these pathogens are categorized as quarantine organisms and are therefore regulated. Phytosanitary measures (PMs) are implemented and one aspect involves diagnostic procedures to detect these pathogens. To date, visual screening of external and internal symptoms is combined with the specific identification of these pests, either through microscopy, biochemical or molecular tests. A disadvantage of all these tests is the requirement of the prior extraction of nematodes from the tubers, which is not suitable for high‐throughput screening. This paper describes the MeloTuber Test developed to simultaneously detect M. chitwoodi and M. fallax by triplex real‐time TaqMan^® PCR directly in secondary potato tuber peelings. DNA extraction is carried out in a 96‐well plate of pooled secondary peelings from one hundred tubers. The analytical sensitivity is such that a single female can be readily detected in such a sample size. The validation data, described here, prove the suitability of this molecular test for the detection of M. chitwoodi and M. fallax in large scale screening tests.     

Relationship between Spongospora subterranea f. sp. subterranea soil inoculum level,host resistance and powdery scab on potato tubers in the field

The relationship between initial soil inoculum level of Spongospora subterranea f. sp. subterranea (Sss) and the incidence and severity of powdery scab on potato tubers at harvest was investigated. In all experiments soil inoculum level of Sss (sporeballs/g soil) was measured using a quantitative real‐time PCR assay. Of 113 commercial potato fields across the UK, soil inoculum was detected in 75%, ranging from 0 to 148 Sss sporeballs/g soil. When arbitrary soil inoculum threshold values of 0, <10 and >10 sporeballs/g soil were set, it was observed that the number of progeny crops developing powdery scab increased with the level of inoculum quantified in the field soil preplanting. In four field trials carried out to investigate the link between the amount of inoculum added to the soil and disease development, disease incidence and severity on progeny tubers was found to be significantly (P < 0·01) greater in plots with increasing levels of inoculum incorporated. There was a cultivar effect in all years, with disease incidence and severity scores being significantly greater in cvs Agria and Estima than in Nicola (P < 0·01).     

Detection of the root lesion nematode Pratylenchus penetrans in potato tubers

The root lesion nematode Pratylenchus penetrans parasitizes a wide range of economically important crops, including potato (Solanum tuberosum). Damage by P. penetrans impacts not only the potato yield but can also reduce the tuber quality. Detailed information on tuber infection by P. penetrans is scarce for most cultivars and molecular detection of nematodes from infected tubers is needed. The objective of this study was to assess tuber symptomatology due to P. penetrans infection in 10 potato cultivars and to provide an accurate molecular methodology for nematode detection using tuber peels. Sprouts of certified potato seed from cultivars Agata, Agria, Camel, Désirée, Dirosso, Kennebec, Laura, Picasso, Royata, and Stemster were planted in 2 L pots, and soil was inoculated with 4 P. penetrans/g of soil. Sixty days after inoculation, tubers were harvested, inspected for lesions, and the number of nematodes/g of potato peel assessed. Observations of tubers with symptoms showed the presence of P. penetrans in superficial layers of peels around the lenticels and injured necrotic tissue. Different nematode stages were detected in tubers of all inoculated cultivars, varying from 4 to 46 nematodes/g of potato peel. Species-specific primers showed suitable sensitivity and reproducibility for the detection of P. penetrans in tuber potato peel samples. The molecular detection of P. penetrans directly from tuber peels can facilitate routine nematode inspections of potato seed tubers or cull potatoes for nematode detection, and prevent further dissemination of this species.     

Improved immunological detection of S<Emphasis Type="Italic">pongospora subterranea</Emphasis>

The genus Spongospora has two members which are important pathogens of vegetables, S. subterranea f.sp. subterranea (Sss) and S. subterranea f.sp. nasturtii (Ssn). The close taxonomic relationship of these formae speciales is based on similar cystosori morphology. The potato disease powdery scab, caused by Sss, is difficult to control. The key control measure is avoidance, aimed at planting clean seed in clean soil. For the development of routine tests for the presence of the pathogen on tubers and in soil, a monoclonal antibody (MAb) was developed using Sss cystosori as immunogen. It detected less than one Sss cystosorus and recognised Sss material from many parts of the world. No cross-reactions with other Plasmodiophoromycetes including Plasmodiophora brassicae, Polymyxa betae, Polymyxa graminis and different Streptomyces species causing common and netted scab of potatoes were observed. A novel tuber sample test method was developed using a kitchen peeling machine. This detected two tubers with one powdery scab lesion each in a sample including eighteen uninfected tubers. When soil samples spiked with cystosori were tested with the MAb, different Sss infestation levels could be discriminated. Ssn cystosori gave absorbance values in ELISA as high as Sss cystosori, whereas fresh crook roots of watercress containing Ssnzoosporangia and plasmodia or mud from an Ssninfected watercress bed gave low absorbance values or no reaction. The potential of these findings for the development of a disease control management are discussed.     

Crop rotation effects on Cyperus rotundus and C. esculentus population dynamics in southern California vegetable production

Control options for Cyperus rotundus and Cyperus esculentus (purple and yellow nutsedge) were evaluated within three cropping systems in the low desert of southern California: (1) standard vegetable crop rotation (weed‐free, uncontrolled nutsedge and cultivation) with spring cantaloupe (Cucumis melo) – summer fallow – winter broccoli (Brassica oleracea), (2) cover crop rotation (halosulfuron and smother crop) with spring wheat (Triticum aestivum)/corn (Zea mays) – summer sudangrass (Sorghum sudanense) – Winter Fallow, (3) rotation with solarization (non‐solarization and solarization) with spring wheat – summer fallow/solarization – winter broccoli. After two growing seasons, broccoli was planted without Cyperus control, to study the effect on yield. Cyperus rotundus tubers increased from 0.66 tubers per m² to 1260 tubers per m² in the uncontrolled treatment over two seasons. Cultivation during the growing season reduced C. rotundus tubers by 93% compared with the uncontrolled plots. Cover crop rotation did not reduce the number of C. rotundus tubers significantly, despite the dense sudangrass canopy shading the soil during most of the summer. Cyperus rotundus was effectively controlled by the solarization treatment. All methods controlled C. esculentus, especially when there were no crops growing in the summer. When broccoli was grown after two years of various management strategies, the cultivation treatment showed a 44% yield reduction compared with the weed‐free control, while the solarization treatment increased broccoli yield by 64% compared with the non‐solarization treatment. Rotations that included sudangrass had low broccoli yield when either C. rotundus or C. esculentus were present.     

Tuber composition in yellow nutsedge (Cyperus esculentus (L.)) variants

Yellow nutsedge variants from California, Georgia, Illinois, Maryland, Minnesota and Oklahoma were analysed for intraspecific differences in tuber composition. Tuber size varied from 70 to 710 mg. Carbohydrates ranged from 45 to 77% of tuber dry weight. Starch was the most abundant carbohydrate in all the tubers. The saccharides, fructose, glucose, sucrose and melibiose were found at least in trace quantities in all the tubers; only tubers of the Georgia and Maryland variants contained significant quantities of all four saccharides, and the other three variants containted principally sucrose. Triglycerides constituted more than 80% of the lipids in the tubers. The major acid present in all tubers was oleic. Composition du tubercule chez divers biotypes de Cyperus esculentus (L.) Des biotypes de Cyperus provenant de Californie, de Géorgie, de l'Illinois, du Maryland, du Minnesota et de l'Oklahoma ont été analysés en vue de rechercher des différences intraspécifiques dans la composition du tubercule. Le poids du tubercule a varié de 70 à 710 mg. Les hydrates de carbone représentaient de 45 a 77% du poids sec du tubercule. L'amidon a été l'hydrate de carbone le plus abondant dans tous les tubercules. Les saccharides: fructose, glucose, saccharose et mélibiose ont été trouvés au moins à l'état de traces dans tous les tubercules; seuls les tubercules des biotypes de Géorgie et du Maryland contenaient des quantités significatives des quatre saccharides et les trois autres biotypes contenaient principalement du saccharose. Les triglycérides constituaient plus de 80% des lipides des tubercules. Le principal acide gras présent dans tous les tubercules était l'acide oléique. Inhaltsstoffe der Knollen verschiedener Herkünfte von Cyperus esculentus (L.) Herkünfte von Cyperus esculentus aus Kalifornien, Gorgia, Illinois, Maryland und Oklahoma wurden auf Unterschiede in ihrer Knollenzusammensetzung untersucht. Die Knollenge-wichte variierten zwischen 70 und 710 mg. Die Kohlenhydratgehalte schwankten von 45 bis 77% des Knollentrockengewichtes. Stärke war in alien Knollen das häufigste Kohlenhydrat. Die Saccharide Fructose, Glucose, Sucrose und Melibiose waren in alien Knollen zumindest in Spuren festzustellen. Lediglich Knollen aus Gorgia und Maryland enthielten größere Mengen aller 4 Saccharide. DieTestlichen 3 Herkünfte enthielten haupt-sächlich Sucrose. Triglyceride bildeten mehr als 80% der Knol-lenlipide. Die häufigste Fettsäure war Ölsäure.     

The yam nematode (Scutellonema bradys), a potential threat to potato (Solanum tuberosum) production in West Africa

Potato (Solanum tuberosum) production in Africa is rapidly expanding and becoming increasingly important. As its geographical production range broadens, so does its potential to host new pests and diseases. Following the discovery that potato can be affected by Scutellonema bradys, further studies were undertaken to assess its potential pathogenicity on potato under screenhouse and field conditions, and on marketed tubers. Potato plants inoculated with S. bradys produced tubers with substantial cracking and evident tuber rot, compared with tubers from uninoculated plants. Symptoms of nematode infection on tubers included a scaly appearance, surface cracking as well as deeper tissue cracks, distortions, and darkened surface patches. In most cases these patches were related to sub‐surface rot. Nematodes were recovered from the soil, roots and tubers of inoculated plants. Eight weeks after inoculation, the reproduction factor of the nematode was greatest (2·0) at the lowest inoculation rate assessed (1000 nematodes per 2·5‐L pot) and least (0·4) at the highest inoculation rate (5000 nematodes per pot). In the screenhouse, potato tuber weights were low and mostly unaffected by nematode inoculation rate, except at 5000 nematodes per pot. In the field, non‐inoculated plants yielded over nine times more tubers than plants inoculated with 2000 S. bradys. Low densities of S. bradys were also recovered from 10 of 15 (67%) samples collected from market stalls, indicating field infection. This study confirms that potato can host and be damaged by S. bradys, raising its prospect as a likely significant biotic constraint to the crop.     

Evaluation of a diagnostic microarray for the detection of major bacterial pathogens of potato from tuber samples

Potato can be infected with many bacterial pathogens, the detection of which is necessary in seed certification. In this study, a diagnostic microarray previously tested for specificity of probes for detecting the potato bacteria causing blackleg and soft rot (Pectobacterium atrosepticum, Pectobacterium carotovorum, and Dickeya spp.), ring rot (Clavibacter. michiganensis subsp. sepedonicus), scab (Streptomyces scabies and Streptomyces turgidiscabies) and brown rot (Ralstonia solanacearum) from pure culture was evaluated for analytical sensitivity when testing directly from tuber samples. The microarray readily detected all the bacterial species when 100 ng of the target bacterial DNA from pure culture was mixed with DNA from soil microbes and potato. However, detection was inconsistent when total DNA isolated directly from infected tubers or enriched bacterial culture was used. While the high specificity of the probes could be confirmed from the results of the DNA cocktail experiment used as a control, the study demonstrated that the level of analytical sensitivity of the microarray under the tested condition was not sufficient to detect bacteria directly from tubers. Therefore, in addition to the cost and organizational complexities, the low analytical sensitivity and limited reproducibility of the microarray are constraints for establishing the platform for routine detection of potato bacterial pathogens from tuber samples.     

Regenerative capacity of rhizomes and tubers from two populations of Helianthus tuberosus L. (Jerusalem artichoke)

The regenerative responses of rhizomes and tubers from two populations of Helianthus tuberosus L. to burial and fragmentation were studied in field experiments. The regeneration of both populations varied with planting depth and stage of growth at which fragmentation occurred. Shoots of both populations emerged from rhizomes or tubers planted to depths of 30 cm. The percentage of tubers that regenerated was higher than that of rhizomes, particularly from deeper planting depths. The regeneration from rhizomes and tubers of a riverbank population was greater than that of a‘weedy’population. Rhizomes and tubers from both populations that had failed to produce shoots I year after planting were found to have decomposed completely. The significance of these results in relation to the distribution and control of H. tuberosus is discussed.     

Re-infection by Erwinia carotovora (Jones) Bergey et al. in Potato Stocks derived from Stem Cuttings1

Propagation of potato stocks by the stem cutting method has produced crops almost entirely free from infection with the soft rot coliform bacteria, Erwinia carotovora (Jones) Bergey et al var. atroseptica (Hellmers et Dowson) Dye and E. carotovora var. carotovora Dye. However, low levels of re-infection have occurred and evidence indicates that a source of the organisms was infected insects. Air-borne spread of bacterial aerosols generated by raindrop impaction on infected stems might also result in healthy stocks becoming re-infected.     

Bacterial diseases of potatoes in the major potato-growing areas in Turkey1

In 1988 and 1989 bacterial diseases of potatoes in Central Anatolia were investigated by utilizing the EC method for the detection of ring-rot bacterium (Clavibacter michiganensis ssp. sepedonicus) and using selective medium. 91 samples containing 200 tubers from commercial and farmers’ stores in Central Anatolia were tested for the presence of C.m.sepedonicus and about 50 tubers of each sample were also tested for the presence of soft-rot erwinias. Five different bacteria that cross-reacted with C.m.spedonicus antisera were isolated from heel-end extracts. All cross-reacted bacteria differed from C.m.sepedonicus morphologically and none of them was pathogenic on eggplant. C.m. sepedonicus was not detected, but Erwinia carotouora ssp. carotouora and Erwinia carotovora ssp. atroseptica were present in 7 and 17% of the samples respectively.     

PCR-based determination of colonization patterns during potato tuber infection by single and multiple pathogens

Potato tubers piled in storage are prone to infection by numerous pathogens. Each pathogen can cause damage alone, but severe losses often arise when more than one pathogen is involved. Currently, only a visual diagnosis is practiced on potato tubers before storing them, which does not allow any prediction of further disease spread. The aim of the present study was to determine differences in patterns of tissue colonization by several tuber decay pathogens and how late blight infection affects further tuber colonization by other important tuber pathogens. This study was conducted using artificial inoculation of potato tubers and PCR to provide an early and accurate diagnosis of disease development for major potato tuber rots, and to assess potential synergism/antagonism between Phytophthora infestans and other pathogens in stored tubers. In order to accurately follow the progress of each pathogen in tuber tissues, samples were collected over time from both the surface (peel, 0–2 mm depth) and internal tissues (flesh, depth > 2 mm) of the tubers at various distances from the inoculation site, at 3, 5, 7, 10, 12, 14, 17, and 19 days after inoculation. Successful detection of single or multiple pathogens was achieved using specific PCR-primers for each pathogen. Pathogens were always detected several centimeters ahead of the visible lesions. This tracking enabled us to determine the extent of colonization both on the tuber’s surface and in internal tissues by each tested pathogen, either after single or multiple infections involving P. infestans as the primary pathogen. The presence of P. infestans was shown to enhance the development of Pectobacterium atrosepticum and to slow down that of P. erythrospetica and Pythium ultimum. No noticeable effect on further tuber colonization by F. sambucinum, V. dahliae or V. albo-atrum was observed in the presence of P. infestans. This approach involving more than one pathogen is more realistic than classical studies considering single pathogens, and may be helpful in monitoring the sanitary status of stored tubers. Our results make the outcome of certain combinations of pathogens in potato tubers more predictable and may result in more efficient preventive measures.     

Investigations on potato mop-top furovirus in Sweden1

Potato mop-top furovirus (PMTV) was isolated for the first time in Sweden in 1985. During 1986 and 1987, soil samples from potato fields, mainly in the south-west of Sweden, were tested for PMTV. The virus was detected in 49 out of 305 samples tested. PMTV was also found to be present in soil collected from potato riddles during potato grading in early spring. The soil samples were tested by using Nicotiana clevelandii and N. debneyi as bait plants in a glasshouse. Seven potato cultivars were grown in a PMTV-infested field. PMTV symptoms in the tubers, i.e. external and/or internal brown rings and arcs (spraing), were observed in cvs Evergood, Provita, Saturna and Ukama but not in cvs Bellona, Bintje or King Edward. Very few, or no, PMTV symptoms were found in tubers of susceptible cultivars when examined 2-3 weeks after lifting. In later examinations spraing appeared and increased. The increase was greater in tubers stored at 9°C than in those at 4°C, and in cut than in uncut tubers.     

<Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> subsp. <Emphasis Type="Italic">carotovorum</Emphasis> can cause potato blackleg in temperate climates

It is well established that the pectinolytic bacteria Pectobacterium atrosepticum (Pca) and Dickeya spp. are causal organisms of blackleg in potato. In temperate climates, the role of Pectobacterium carotovorum subsp. carotovorum (Pcc) in potato blackleg, however, is unclear. In different western and central European countries plants are frequently found with blackleg from which only Pcc can be isolated, but not Pca or Dickeya spp. Nevertheless, tubers vacuum-infiltrated with Pcc strains have so far never yielded blackleg-diseased plants in field experiments in temperate climates. In this study, it is shown that potato tubers, vacuum-infiltrated with a subgroup of Pcc strains isolated in Europe, and planted in two different soil types, can result in up to 50% blackleg diseased plants.     

Effect of glyphosate on the sprouting of Cyperus rotundus L. tubers

Post-emergence applications of glyphosate [N-(phosphonomethyl)glycine] have been shown not to eradicate purple nutsedge (Cyperus rotundus L.) in the field. It was not known if this was due to failure to control emerged plants or if dormant tubers produced new plants after application. Studies with individual plants were conducted in screenhouse facilities to determine the effects of glyphosate rate, time for translocation, area of foliage treated, and shade on the sprouting ability of tubers attached to treated plants. Rates of 1.5–2.0 kg/ha glyphosate inhibited tuber sprouting; 72 h were required for complete translocation at 1.0 kg/ha whereas 36 h were sufficient at 2.0 kg/ha. Treating less than all of the foliage reduced foliar control and increased tuber sprouting. Shading treated plants reduced control of the foliage but did not affect glyphosate translocation to the tubers. These studies showed that glyphosate kills C. rotundus foliage and the tubers attached to treated plants. Therefore, regrowth after glyphosate application under field conditions is due to dormant tubers which sprout after treatment.