High Field Resistance Research Articles

Effect of magnetic impurities on electronic transport of heterogeneous ferromagnets

Electronic transport in granular Co-Ag films is studied between subhelium and room temperatures in fields up to 16 T. A number of unusual properties are found including a strong variation of magnetoresistance at low temperatures and sublinear ${(d}^{2}{R/dT}^{2}l0)$ temperature dependence of high field resistance above 50 K. We show that paramagnetic impurities or small magnetic clusters embedded in the normal-metal matrix influence significantly the electronic transport in heterogeneous ferromagnets. The effect is strongly enhanced as compared with paramagnetic impurities in homogeneous normal metals, and is comparable and even superior over the phonon scattering up to room temperatures. This mechanism is argued to be responsible for the peculiar properties of resistance and magnetoresistance of granular ferromagnets.

IPR 82-Araucária, cultivar de batata para olericultura sustentável

São apresentadas as principais características agroindustriais e morfológicas de uma nova cultivar de batata lançada pelo IAPAR, em parceria com a Embrapa Hortaliças, Brasília (DF) e a Embrapa Semente Básica, Canoinhas (SC). "IPR 82-Araucária" foi selecionada de populações clonais introduzidas do CIP, Lima-Peru, por meio da Embrapa Hortaliças e avaliada nas Estações Experimentais do IAPAR desde 1984. A nova cultivar apresentou como fatores positivos alta produtividade comercial e resistência de campo à requeima, permitindo prever reduções em até 50% no uso de fungicidas para o controle da doença. A suscetibilidade à mancha chocolate e sarna comum evidenciaram a necessidade de manejo adequado de densidade e época de plantio, calagem e irrigação para minimizar os riscos de ocorrência dessas doenças. Com essas características, "IPR 82-Araucária" apresenta potencial para atender às demandas de produtores orgânicos e para produção em áreas de mananciais de água.

Bandstructure effect on high-field transport in GaN and GaAlN

The velocity-field characteristics in zinc-blende GaN are calculated from the Boltzmann equation, using realistic energy bands taken from ab initio theory. The drift velocity and the high-field negative differential resistance are shown to be largely determined by the inflection point in the bands centered around the Γ valley, instead of the usual intervalley scattering. We analyze the relative importance of these competing mechanisms for GaN and Al0.5Ga0.5N. The importance of this anomaly to device properties is also discussed.

Components of resistance of cassava to African cassava mosaic virus

Components of resistance of cassava (Manihot esculenta) to African cassava mosaic virus (ACMV) and their interrelationships were confirmed and quantified in a series of experiments at Adiopodoume (Ivory Coast, West-Africa). The response to virus infection and toBemisia tabaci infestation of a large collection of cassava, including local cultivars and others derived from inter-specificM. glaziovii hybrids was assessed. A consistent correlation was found between virus titre, symptom intensity, disease incidence and non-systemicity (recovery) which suggests that they are different expressions of the same genetic resistance. By contrast, there was no correlation between whitefly infestation and incidence of ACMV, suggesting that resistance to virus and vector are determined by two distinct genetic mechanisms. Several improved cultivars derived from inter-crossing cassava withM. glaziovii as well as some local cultivars were highly resistant and combined low susceptibility, low symptom intensity, low virus content and high level of recovery. Although yield losses ranged from 10% to 30% in such resistant cultivars, the combined effect of high field resistance and high rate of recovery lead to low disease incidence and limited yield losses, even in areas of high infection pressure such as Adiopodoume.

SEX-SPECIFIC COSTS OF RESISTANCE TO THE FUNGAL PATHOGEN USTILAGO VIOLACEA (MICROBOTRYUM VIOLACEUM) IN SILENE ALBA.

Costs of resistance are often invoked to explain the maintenance of polymorphisms for resistance to fungal pathogens in natural plant populations. To investigate such costs, 27 half-sib families of Silene alba, collected from a single host population, were grown in experimental populations in the presence and absence of the anther-smut fungus Ustilago violacea, a host-sterilizing pathogen transmitted by insects that are both pollinators and vectors of the disease. Host families differed significantly in resistance to inoculation, indicating the presence of genetic variation for mechanisms that impede fungal growth once the disease is encountered ("biochemical" resistance) within the host population. In addition, host families differed significantly in onset of flowering and in flower production in the absence of the disease. Path analysis revealed that late onset of flowering in male host families made a direct contribution to high field resistance (P < 0.01), probably due to a reduced rate of contact between hosts and vectors carrying high spore loads (avoidance, or "phenological" resistance). The contribution of low flower production to field resistance only approached significance (P < 0.10). There was a significantly positive genetic association between biochemical and phenological resistance, suggesting that delayed flowering is either a pleiotropic effect of biochemical resistance, or that genes governing these traits are in linkage disequilibrium. Path analysis revealed that biochemical resistance made both a direct contribution to field resistance (P < 0.01) and a positive indirect contribution via its association with phenology and flower production (P < 0.05) in male hosts. Costs of resistance were sex specific. Male host families with high field resistance had significantly lower reproductive success in healthy populations, indicating a fitness cost of field resistance (P < 0.01), whereas no costs were detected for female hosts. Path analysis revealed that the biochemical component of field resistance made no direct contribution to the observed fitness cost in male hosts, whereas its indirect effect through phenology was only marginally significant (P < 0.10). This finding indicates that fitness costs were mainly due to the phenological component of field resistance. Because the host population had no known history of disease, it is not clear whether the fitness costs are responsible for maintenance of the resistance polymorphism or whether the polymorphism is present for reasons unrelated to pathogen infection. Interactions between host families and pathogen strains with respect to inoculation success were not significant. Hence, there was no evidence for indirect costs of biochemical resistance, that is, reduced resistance to alternative strains. Infection rates in experimental populations with an initially patchy distribution of the pathogen were lower than in populations with a uniform pathogen distribution, suggesting that the effective pathogen pressure and hence the relative success of susceptible and resistant individuals may, in addition to fitness costs of resistance, depend on the spatial population structure of the pathogen.

Quantitative field resistance of wheat to powdery mildew and defense reactions at the seedling stage: identification of a potential marker

Quantitative field resistance of winter wheat ( Triticum aestivum L.) to powdery mildew ( Erysiphe graminis DC f. sp. tritici ÉM) is an important trait that is selected for by plant breeders. Due to the necessary assessment in the field, the estimation of quantitative field resistance is very expensive and time-consuming. Therefore, the availability of easily scorable markers for this trait would be of great advantage in wheat breeding. In this study, host-responses that can be scored on individual plants at the seedling stage were assessed to see if they could serve as markers for quantitative resistance in the field. The accumulation characteristics of five defence-related gene transcripts and the formation of papillae and cell wall appositions following an infection by powdery mildew were compared in six wheat lines and one spelt ( Triticum spelta L.). The lines represented a broad spectrum of different degrees of quantitative field resistance but carried no effective major resistance gene against powdery mildew. No clear correlation was found between the kinetics of levels of accumulation of defence-related gene transcripts following infection at the seedling stage and the degree of quantitative field resistance. However, cytological analysis showed that the proportion of adaxial epidermal cells that responded to pathogen attack by the formation of papillae or cell wall appositions appeared to be an indicator of high quantitative field resistance. In lines exhibiting a high quantitative field resistance, more than 80% of attacked adaxial cells responded, while in the more susceptible lines, this value dropped to less than 20%. Thus, the easily scorable proportion of attacked cells that show no cytologically visible host-response may provide a valuable marker to predict the degree of quantitative field resistance.

Ac brador: a new late-maturing cultivar with a high degree of field resistance to late blight

AC Brador is a late maturing yellow-fleshed cultivar. The vine maturity is slightly later than Russet Burbank. The oblong tubers have a specific gravity which is slightly higher than Kennebec. The boil and bake quality of AC Brador is similar to Kennebec. The mean French fry quality of AC Brador is below that of Russet Burbank but still in the acceptable range. This cultivar has extremely high field resistance to late blight resistance to verticillium wilt and early blight, a relatively high resistance to PLRV, and a moderate resistance to PVYand rhizoctonia.

The effect of current, illumination and contact nature on equilibration between bulk and edge current-carrying states

The form of the high-field spin-resolved Shubnikov-de Haas resistance maxima in a high-mobility GaAs-(Ga,Al)As heterojunction 2D electron gas is shown to be strongly dependent on current, illumination time and the nature of the voltage contacts. The effects of increasing current and illumination time are very similar, with both reducing the influence of the contact nature. The similarity is attributed to a common modification of the edge potential in the device due to a change in the device electrostatics. At saturation illumination the current dependence is found to be wholly absent. The edge-bulk scattering length calculated from the theory of the current dependence of the maxima is found to be strongly dependent on the type of voltage contact used, indicating that this value does not reflect a fundamental bulk property. We also observe contact-specific fine structure in the N=1 high-field maximum, which is attributed to fluctuations in the transmission coefficients of the voltage probes.

Effect of Phytophthora infestans infection on superoxide dismutase dependent cytochrome c—reducing activities of leaves as related to resistance of potato plants to late blight

The time-course and phenomenology of superoxide production during compatible and incompatible interactions of the potato, Phytophthora infestans system were studied in the potato plants grown in ‘aseptic’ conditions by assaying superoxide dismutase-inhibited cytochrome c reducing active after fungal penetration were dependent onthe plant susceptibility to P. infestans. Superoxide dismutase-sensitive cytochrome c reducing activity was also found in both leaf tissues and diffusates 17–20 h after infection of potato plants by compatible races of P. infestans. The pattern of O 2 ⨪ -production in cultivars having high field resistance to late blight was shown to be similar to that in incompatible interactions. The participation of activated oxygen species in vertical and horizontal resistance of potato plants are discussed.

Yield losses of soybeans due to Phytophthora megasperma f.sp. Glycinea

Field trials were conducted in two seasons to determine the influence of Phytophthora megasperma f.sp. glycinea on seed yields of soybean genotypes with different levels of resistance. The fungicide metalaxyl, applied as a seed dressing and soil drenches, was used to control the disease. The cultivar Davis, which has high field resistance, did not suffer significant losses in either year. whereas the yield depression of less resistant genotypes ranged up to 72%, depending on the genotype and year. In 198 1 - 82 high death rate of plants occurred early in the season, but yield losses were less than in 1982-83 when mortality occurred late in the season. The declining ability of surviving plants to compensate for disease losses during the latter growth stages may account for the differences in yield losses between seasons.Genotypes with immunity to P. megasperma f.sp. glycinea have been widely grown in the United States because they offer complete protection against some races. However, new pathogenic races have developed quickly, and previously immune genotypes have then suffered severe yield losses. The results of these trials demonstrate that yield losses can be prevented without resorting to fungicide treatments. It is likely that a stable long-term solution to phytophthora root and stem rot will be conferred by field resistance.

Krantz: A Russet cultivar for the irrigated sands

Krantz is an oblong to slightly blocky, russet-skinned potato cultivar with medium-late maturity and a vigorous vine. It is resistant to hollow heart, has high resistance to common scab and possesses high field resistance to late blight. It is moderately resistant toVerticillium wilt, susceptible to early blight, viruses S and X, and exhibits symptoms of bacterial ring rot. Krantz is adapted to the irrigated sands, but will growth crack in heavier soils.

Studies of Marssonina castagnei in Australasia

AbstractComparative studies of conidium morphology and host range and pathogenicity tests of Australian and New Zealand isolates of Marssonina castagnei in the laboratory established their equivalence which was indicative of a common origin. It is speculated that trans‐Tasman dispersal is responsible for the introduction of M. castagnei into New Zealand and its widespread distribution. This is based on the prior recording of M. castagnei in Australia, the potential of M. castagnei conidia for long distance transport and the proven records of trans‐Tasman dispersal of other pathogens. Laboratory inoculations and field observations showed P. alba cv. Silver poplar and its hybrids to be highly susceptible to M. castagnei. Populus alba X P. glandulosa hybrids and Italian selections of P. alba showed high field resistance.

Cotton Resistance to the Root Knot‐Fusarium Wilt Complex. II. Relation to Root‐Knot Resistance and its Implications on Breeding for Resistance1

The fusarium wilt fungus, Fusarium oxysporum Schlect f. vasinfectum [(Atk.) Synd.&amp; Hans.], and the root‐knot nematode (RKN) [Meloidogyne incognita (Kofoid &amp; White) Chitwood] cause a destructive disease complex in cotton (Gossypium hirsutum L.). This study was conducted to determine the range of genetic resistance to RKN in a group of 18 cotton cultivars and breeding lines, to evaluate the relationship between genes for resistance to fusarium wilt disease (FW) and the genes for RKN resistance, and to ascertain the relative importance of the two types of resistance in controlling FW. Numbers of RKN eggs produced on the cottons ranged from &lt;1000/plant on Auburn 623 RNR to &gt;148 000/plant on ‘Rowden’. One‐eighth as many and 18 times more RKN eggs/plant were produced on Auburn 623 RNR and Rowden in 40 days, respectively, than were used to inoculate them. No commercial cultivar was resistance to RKN in this study. Two cotton cultivars expressed genetic resistance that provided moderate field resistance to FW independently of RKN resistance. Differences in resistance to FW in the field among cotton cultivars and breeding lines were determined more by RKN resistance than by genetic resistance to FW. Results indicate that cotton can be developed with genetic resistance to FW independently of RKN resistance and that this genetic resistance probably would provide moderate field resistance to FW. High field resistance to the RKN‐FW complex depends on high RKN resistance, and cotton cultivars with high RKN resistance probably would have adequate field resistance to this complex even if they were genetically susceptible to FW.

Cotton Resistance to the Root Knot‐Fusarium Wilt Complex. I. Relation to Fusarium Wilt Resistance and its Implications on Breeding for Resistance1

Fusarium wilt disease (FW) caused by Fusarium oxysporum Schlect f. vasinfectum [(Atk.)Synd. &amp; Hans.] and root‐knot nematodes (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] cause a major disease complex affecting cotton (Gossypium hirsutum L.). The purpose of this study was to determine the efficacy of using resistance to FW in the vascular system of plants grown in a greenhouse as a criterion for selecting cotton plants that are resistant to FW in the RKN‐FW complex as it occurs in the field. Eighteen cotton cultivars and breeding lines were inoculated in a greenhouse by injecting spores of the FW fungus directly into stems. Incidence of FW ranged from 29 to 82%. The FW percentages of the 18 cotton cultivars and lines in a field infested with both the fungus and RKN ranged from 3 to 99%. Results indicated that stem vascular resistance to FW was probably independent of any mechanism of resistance that might have prevented fungal invasion of the vascular system and that differences in vascular resistance were probably genetically controlled. Vascular resistance observed in the greenhouse failed to discriminate between differences in FW resistance among several cottons when grown in the field. This and other evidence presented indicated that a low probability of success would be expected for developing cotton cultivars with high field resistance to FW in the RKN‐FW complex by either selecting for vascular resistance expressed in plants grown in a greenhouse or through field selection by present techniques. Field selection for many decades had resulted in development of moderately resistant cultivars but had not been successful in developing highly FW‐resistant cultivars. Further progress by the field selection method may be possible in the future, if genes for higher resistance, such as in breeding line Auburn 623 RNR, are used and more precise screening techniques can be developed.

Linkage groups of field resistance genes of upland rice variety "Sensho" to leaf blast caused by Pyricularia oryzae Cav.

The upland rice variety Sensho has a high field resistance (quantitative resistance) to leaf blast that seems to be stable in response to the c.hanges in the pathogenicity of the blast fungus (Pyricularia oryzae CAv.). Some resistant cultivars of paddy rice have been developed using varieties derived from Sensho, but their resistance levels are not as high as that of Sensho. For further use of the high field resistance, it is necessary to study the mode of inheritance of the resistance. In the present study, linkage groups of the resistance genes of Sensho were studied using linkage testers with marker genes (Table 1). Leaf blast resistance and marker genes were investigated in F3 lines derived from twelve crosses between the linkage testers and Sensho. Leaf blast resistance was estimated by nursery tests and marker genes were stuclied by using the phenotype of F3 lines in paddy fields. F3 lines were divided into three groups ; tester type group (example, la), segre-gating group (la/+) and Sensho type group (+). Linkage relation was tested by t-test for the difference of means of leaf blast score between the tester type group and the Sensho type group.

Guidelines for finer lines in thick film circuitry : P. J. B. Bertrams, W. Keuper, G. Koch and J. H. C. van Mourik. Electrocomponent Sci. Technol.10, 237 (1983)

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH4–H2 gas mixture (1–7%) at approximately 560 °C substrate temperature. The growth rate ranged between 0.9 μm/h and 2.2 μm/h, microwave powers between 520 W and 720 W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

Automated thermal reliability analysis of hybrids : Gerald N. Morrison and Sally M. Moite. Proc. A. Reliab. Maintainab. Symp. 251 (1983)

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH4–H2 gas mixture (1–7%) at approximately 560 °C substrate temperature. The growth rate ranged between 0.9 μm/h and 2.2 μm/h, microwave powers between 520 W and 720 W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

DORMIE KENTUCKY BLUEGRASS

Dormie is a cultivar of Kentucky bluegrass (Poa pratensis L.) with a high field resistance to LTB snow mold. It is specially suited for use in amenity turf in the low snowfall areas of the prairie region.

A survey of Ribes species for aphid resistance

SUMMARYField surveys from 1967 to 1970 of a Ribes species collection comprising ninety‐five plants representing fifty‐six species and fourteen sections of the genus, revealed moderate or severe aphid infestations as follows: Hyperomyzus lactucae (L.) on ten species included in five sections; H. pallidus H.R.L. ten species, two sections; Nasonovia ribisnigri (Mosley) twenty‐eight species, seven sections; Aphis grossulariae Kltb. twenty‐two species, ten sections; Cryptomyzus ribis (L.) four species, two sections; C. korschelti Börner three species, two sections.Cut shoot tests suggested that c. 50% of sixty‐three field‐resistant accessions were tissue‐susceptible to H. lactucae, and about 70% of fifteen field‐resistant types were tissue‐susceptible to N. ribisnigri. Possible field escape mechanisms are discussed.In breeding black‐currants resistant to H. lactucae and gooseberries resistant to N. ribisnigri, the donors R. sanguineum and R. cereum, and R. roezlii, respectively, were chosen for their high field and tissue resistance and for the known, or expected, fertility of their F1 hybrids with black‐currant and gooseberry.

Vaccinium Clones Resistant to Phytophthora cinnamomi1

Abstract Two clones of Vaccinium showed high field-resistance to Phytophthora cinnamomi and remained unaffected during 3 years of observation in naturally infested soil: Me-US 32, a productive, cultivated highbush selection (V. australe), and a selection from the wild of the diploid species (V. atrococcum). However, the clone, E-22 selection of V. australe, growing in adjacent row to the resistant clones was severely damaged by the pathogen. Phytophthora cinnamomi was readily isolated from soil surrounding both resistant and susceptible clones.