Yield of ‘Superior’ potatoes (Solanum tuberosum) and dynamics of root-lesion nematode (Pratylenchus penetrans) populations following “nematode suppressive” cover crops and fumigation

De 1992 à 1996, des études ont été menées à Simcoe, Ontario, pour évaluer diverses espèces de cultures de couverture comme alternatives possibles à la fumigation précédant la culture de la pomme de terre (Solanum tuberosum). Le seigle (Secale cereale), une culture de couverture hivernante fréquente dans les systèmes de production de légumes, est un excellent hôte pour le nématode des lésions racinaires (Pratylenchus penetrans) et lui procure un hôte convenable pour hiverner dans les sols sableux grossiers. Les fumigants Vorlex Plus CP et Telone IIB ont été comparés à la moutarde ‘Domo’ (Brassica juncea) pour les années 1993 et 1994 de production de pommes de terre. Le seigle mélangé au trèfle rouge (Trifolium pratense) a été inclus en tant que système connu de culture de couverture hôte. Les plantes cyanogénétiques telles la moutarde ‘Domo’ (1994) ou la moutarde ‘Cutlass’ (1995, 1996), le canola ‘Forge’ (Brassica rapa), les hybrides sorgho/sorgho herbacé ‘Sordan 79’ et ‘Trudan 8’ (Sorghum bicolor) et le lin (Linum usitatissimum) ont été comparées au fumigant Vorlex Plus CP et au sorgho ‘NK557’ (Sorghum vulgare) quant à leurs effets sur les rendements de la pomme de terre et sur les nématodes. Une fumigation superficielle (15 cm) et une en profondeur (45 cm) avec le Vorlex Plus CP ont aussi été comparées pour les années 1994 à 1996 de production de pommes de terre. Il y avait peu de différence de décelable entre tous les traitements en pourcentage ou en jours pour atteindre 50 % d’émergence des pommes de terre. Les rendements totaux et vendables les plus élevés ont été obtenus avec la fumigation au Telone IIB, puis avec la fumigation au Vorlex Plus CP et la moutarde ‘Domo’, suivis du traitement témoin et de la couverture de seigle et de trèfle rouge. Les populations de nématodes ont dépassé le seuil de 1000 kg-1 de sol pour tous les traitements et étaient les plus élevées pour les pommes de terres qui suivaient la couverture de seigle et de trèfle rouge. Les rendements et la répression des nématodes avec les hybrides sorgho/sorgho herbacé et les moutardes semblaient intermédiaires entre la fumigation et la non-fumigation. Toutes les cultures de couverture semblaient être des hôtes au champ pour le nématode des lésions racinaires et la réduction des niveaux des populations n’apparaît que lorsque intervient la destruction par l’hiver. La mortalité des nématodes était excellente avec la fumigation et n’était surpassée que par la mortalité hivernale après incorporation de ‘Sordan 79’. L’emploi du ‘Sordan 79’ pendant au moins une partie de l’été suivi de son incorporation a été une alternative à la fumigation précédant la culture de la pomme de terre. Le passage en profondeur d’un chisel semble réduire les populations de nématodes probablement par un effet physique. Là où les populations de nématodes le justifient, une fumigation en profondeur avant la culture de la pomme de terre semble de mise.Studies were conducted at Simcoe, Ontario from 1992 to 1996 to evaluate various cover crop species as possible alternatives to fumigation prior to potatoes (Solanum tuberosum). Cereal rye (Secale cereale), a common overwinter cover crop in vegetable production systems, is an excellent host for the root-lesion nematode (Pratylenchus penetrans) and provides a suitable overwintering host on coarse sandy soils. Vorlex Plus CP and Telone IIB fumigants were compared to 'Domo' mustard (Brassica juncea) for the 1993 and 1994 potato crop years. Rye plus red clover (Trifolium pratense) was included as a known host cover crop system. Cyanogenic plants including 'Domo' mustard (1994) or 'Cutlass' mustard (1995, 1996), 'Forge' canola (Brassica rapa), 'Sordan 79' and 'Trudan 8' sorghum-sudangrass hybrids (Sorghum bicolor), and flax (Linum usitatissimum) were compared to Vorlex Plus CP fumigant and 'NK557' sorghum (Sorghum vulgare) for effects on potato yield and nematodes. Shallow (15 cm) and deep (45 cm) fumigation with Vorlex Plus CP were also compared prior to potatoes for the 1994 to 1996 crop years. There was little detectable difference in percent or days to 50% emergence of potatoes following any treatment. Highest total and marketable yields resulted from Telone IIB fumigation, then Vorlex Plus CP fumigation and 'Domo' mustard, followed by control and rye plus red clover cover. Populations of nematodes surpassed the threshold of 1000 kg-1 soil in all treatments and were highest in potatoes following rye plus red clover. Yield and nematode control following sorghum-sudangrass hybrids and mustards appeared to be intermediate between fumigated and not fumigated. All of the cover crops appeared to be root-lesion nematode hosts in the field, and reduction of population levels appeared to result after incorporation or nematode winterkill. Nematode mortality was excellent with fumigation and next best from kill over the winter after 'Sordan 79' incorporation. 'Sordan 79' grown over at least part of the summer followed by incorporation was an alternative to fumigation prior to potatoes. Deep chiselling appears to reduce nematode population, possibly by physical action. Where nematode populations warrant, deep fumigation prior to potatoes appears to be of merit

Inhibition of Pratylenchus penetrans by intercroping of Rudbeckia hirta and Lycopersicon esculentum in pot cultivation

Dans la culture en pot en serre chaude sur une période de 6 semaines, la densité de population du Pratylenchus penetrans a diminué sévèrement avec Rudbeckia hirta seul et avec un mélange de R. hirta et de tomate, tandis que la tomate seule a supporté la population de nématodes. La réduction de population est attribuée en partie à l'effet nématicide connu du thiarubrine C de R. hirta. De façon générale, la présence du R. hirta dans le pot de tomate a simplement supprimé légèrement la croissance de l'une ou l'autre des plantes durant les 6 semaines.In greenhouse pot culture over a 6-week period, population density of Pratylenchus penetrans declined pronouncedly both under Rudbeckia hirta alone and under a R. hirta - tomato combination, whereas tomato alone supported the nematode population. Population reduction is attributed in part to the known nematicidal effect of thiarubrine C in R. hirta. Overall, the presence of R. hirta in the tomato pot only slightly suppressed growth of either plant during the 6 weeks

Fluctuations of populations of the pin nematode Paratylenchus projectus under selected potato management practices

Des expériences sur la distribution et la survie du nématode de goupille Paratylenchus projectus dans des systèmes de production de pomme de terre et sur son contrôle par divers mécanismes sont décrites. Les meilleures stratégies de gestion pour le nématode de goupille incluent l'utilisation du lin textile ou d'une moutarde ou canola à haut-glucosinolate, l'utilisation de 'Trudan 8' sudangrass comme ajout de matière organique dans le sol, et le labourage peu profond mais complet d'un sol sablonneux en automne ou au début du printemps pour perturber le sol. En général, plusieurs graminées et légumineuses devraient être évitées comme cultures de protection.Experiments on the distribution and survival of pin nematode Paratylenchus projectus in potato growing systems and on its control by various mechanisms are described. Preferable management strategies for the pin nematode include the use of flax or a high-glucosinolate mustard or canola, the use of 'Trudan 8' sudangrass to add organic matter into the soil, and shallow but thorough tillage of a sandy soil in the fall or in early spring to disrupt the soil. In general, many grasses and legumes should be avoided as cover crops

A note on the occurrence of root lesion nematodes under native sand-prairie plant species in the Regional Municipality of Haldimand-Norfolk, Ontario

Le nématode des lésions des racines (Pratylenchus penetrans), le nématode phytoparasite le plus important du sud de l'Ontario, possède une gamme d'hôtes extrêmement large. À cause de la nécessité de réprimer ces parasites avec des cultures recouvrantes qui sont peu ou pas hôtes, plusieurs espèces indigènes des prairies sablonneuses ont été évaluées pour leur susceptibilité au nématode des lésions. Onze espèces appartenant à quatre familles (Asclepiadaceae, Asteraceae, Poaceae et Fabaceae) ont été identifiées commes des hôtes faibles. Les populations très faibles de P. penetrans sur ces espèces indiquent qu'elles pourraient avantageusement servir comme cultures recouvrantes.The root lesion nematode Pratylenchus penetrans, which is the most important plant-parasitic nematode in southern Ontario, has an extremely wide host range. Because of the need to suppress lesion nematodes with cover-crop species which are poor or non-hosts of this parasite, a number of native sand-prairie species were evaluated for susceptibility. Eleven plant species belonging to the families Asclepiadaceae, Asteraceae, Poaceae and Fabaceae were determined to support very low numbers of P. penetrans and consequently to have potential as beneficial cover-crops

Couples affected by dementia and their experiences of advance care planning: A grounded theory study

Global policy places emphasis on the implementation and usage of advance care planning (ACP) to inform decision making at the end of life. For people with dementia, where its use is encouraged at the point of diagnosis, utilisation of ACP is relatively poor, particularly in parts of Europe. Using a constructivist grounded theory methodology this study explores the ways in which co-residing couples considered ACP. Specifically it seeks to understand the ways in which people with dementia and their long-term co-residing partners consider and plan, or do not plan, for the future medical and social care. Sixteen participants were interviewed. They identified the importance of relationships in the process of planning alongside an absence of formal service support and as a result few engaged in ACP. The study recognises the fundamental challenges for couples in being obliged to consider end of life issues whilst making efforts to ‘live well’. Importantly the paper identifies features of the ACP experience of a relational and biographical nature. The paper challenges the relevance of current global policy and practice, concluding that what is evident is a process of ‘emergent planning’ through which couples build upon their knowledge of dementia, their networks and relationships and a number of ‘tipping points’ leading them to ACP. The relational and collective nature of future planning is also emphasised

The Cryogenic Target for the G0^0 Experiment at Jefferson Lab

A cryogenic horizontal single loop target has been designed, built, tested and operated for the G$^0$ experiment in Hall C at Jefferson Lab. The target cell is 20 cm long, the loop volume is 6.5 l and the target operates with the cryogenic pump fully immersed in the fluid. The target has been designed to operate at 30 Hz rotational pump speed with either liquid hydrogen or liquid deuterium. The high power heat exchanger is able to remove 1000 W of heat from the liquid hydrogen, while the nominal electron beam with current of 40 $\mu$A and energy of 3 GeV deposits about 320 W of heat into the liquid. The increase in the systematic uncertainty due to the liquid hydrogen target is negligible on the scale of a parity violation experiment. The global normalized yield reduction for 40 $\mu$A beam is about 1.5 % and the target density fluctuations contribute less than 238 ppm (parts per million) to the total asymmetry width, typically about 1200 ppm, in a Q$^2$ bin.Comment: 27 pages, 14 figure

The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method

Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering

We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 = 0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state, and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A_n provides a direct probe of the imaginary component of the 2-gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened to meet PRL length limit, clarified some text after referee's comment

Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange quark contributions to the currents of the proton. The measurements were made at JLab using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate non-zero, Q^2 dependent, strange quark contributions and provide new information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure

Strangeness in the Nucleon on the Light-Cone

Strange matrix elements of the nucleon are calculated within the light-cone formulation of the meson cloud model. The $Q^2$ dependence of the strange vector and axial vector form factors is computed, and the strangeness radius and magnetic moment extracted, both of which are found to be very small and slightly negative. Within the same framework one finds a small but non-zero excess of the antistrange distribution over the strange at large $x$. Kaon loops are unlikely, however, to be the source of a large polarized strange quark distribution.Comment: 22 pages revtex, 7 postscript figures, accepted for publication in Phys. Rev.