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CENH3 is a centromere-specific histone H3 variant essential for kinetochore assembly. Despite its central role in centromere function, there has been no conclusive evidence supporting CENH3 as sufficient to determine centromere identity. To address this question, we artificially targeted Drosophila CENH3 (CENP-A/CID) as a CID-GFP-LacI fusion protein to stably integrated lac operator (lacO) arrays. This ectopic CID focus assembles a functional kinetochore and directs incorporation of CID molecules without the LacI-anchor, providing evidence for the self-propagation of the epigenetic mark. CID-GFP-LacI-bound extrachromosomal lacO plasmids can assemble kinetochore proteins and bind microtubules, resulting in their stable transmission for several cell generations even after eliminating CID-GFP-LacI. We conclude that CID is both necessary and sufficient to serve as an epigenetic centromere mark and nucleate heritable centromere function. 相似文献
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S.?StamatiadisEmail author C.?Christofides C.?Tsadilas V.?Samaras J.?S.?Schepers D.?Francis 《Precision Agriculture》2005,6(4):399-411
Bare soil reflectance from airborne imagery or laboratory spectrometers has been used to infer soil properties such as soil texture, organic matter, water content, salinity and crop residue cover. However, the relation of soil properties to reflectance data often varies with soil type and conditions and surface reflectance may not be representative of the conditions in the root zone. The objectives of this study were to assess the soil reflectance data obtained by ground-based sensors and to model soil properties in the root zone as a function of surface soil reflectance and plant response. Ground-based sensors were used to simultaneously monitor soil and canopy reflectance in the visible and near-infrared (VNIR) along six rows and in two growth stages in a 7 ha cotton field. The reflectance data were compared to soil properties, leaf nutrients and biomass measured at 33 sampling positions along the rows. Brightness values of the blue and green bands of soil reflectance were better correlated to soil water content, particulate organic matter and extractable potassium and phosphorus, while those in the red and NIR bands were correlated to soil carbonate content, total nitrogen, electrical conductivity and foliar nutrients. The correlation of red soil reflectance with canopy reflectance was significant and indicated an indirect inverse relationship between soil fertility and plant stress. The integration of surface soil reflectance and plant response variables in a multiple regression model did not substantially improve the prediction of soil properties in the root zone. However, crop nutrient status explained a significant portion of the spatial variability of soil properties related to nitrification processes when soil reflectance did not. The implication of these findings to agricultural management is discussed. 相似文献
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H. T. A. M. Schepers 《European journal of plant pathology / European Foundation for Plant Pathology》1984,90(6):247-256
An inquiry was held in 1982, 1983 and 1984 to collect information on the survival and dispersal of cucumber powdery mildew. Growers who planted a crop in December, January or February were asked when they observed mildew for the first time in their crop. A gradual increase in the number of infected crops was observed from planting until May. The earliest observations of infected crops were immediately after planting. The weeks of the first observation of mildew, the disease-free periods and the apparent rates of increase of infected crops are presented for various districts. In the districts with the highest crop density (Pijnacker), mildew was generally observed early in the growing season, while the apparent rate of increase of infected crops was higher than in other districts. In the district with the lowest crop density (Northern Netherlands), mildew was observed late in the growing season and the apparent rate of increase of infected crops was low. Possible means of survival and dispersal of inoculum are discussed. It is suggested that overwintering of inoculum is possible because cucumber plants are grown all year round. Dispersal of cucumber powdery mildew is suggested to take place by transportation of infected planting stock, visitors and wind. 相似文献
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Early ventures into site-specific management involved fertilizer management decisions based on soil chemical properties characterized by some form of grid sampling. This is both labor and capital intensive and practitioners quickly began investigating other methods to get a measure of spatial variability. Aerial photographs, which were mainly used to evaluate and assess crop status, allow for the collection of whole-field data at relatively low cost. Our objective is to determine what relationships exist between aerial spectral data and intensive grid soil test results and whether this information can be used to improve future soil sampling strategies. Soil-test organic matter (OM) and Bray-1 P concentrations were measured on soil samples taken using an alternating 12.2- by 24.4-m grid in late March 1994 from a quarter section under center pivot irrigation. Spectral data were collected in the spring of 1996 prior to planting using a multispectral network of digital cameras. Correlations of brightness values from the blue, green, and NIR bands with both OM and Bray-1 P were significant, but relatively low. Normality tests revealed that brightness values for the spectral data sets were generally evenly distributed while those of the soil test OM and Bray-1 P were positively skewed. Many of the very high soil-test data values were due to past management. When those values were removed from the database, greater correlations between spectral data and soil test data were obtained. These results substantiated that aerial imagery can be used to improve sampling strategies, but it must be used in conjunction with existing knowledge and past management histories. 相似文献
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Comparison of passive and active canopy sensors for the estimation of vine biomass production 总被引：1，自引：0，他引：1
Stamatis Stamatiadis Dimitris Taskos Eleftheria Tsadila Calliopi Christofides Christos Tsadilas James S. Schepers 《Precision Agriculture》2010,11(3):306-315
Recent advances in optical designs and electronic circuits have allowed the transition from passive to active proximal sensors.
Instead of relying on the reflectance of natural sunlight, the active sensors measure the reflectance of modulated light from
the crop and so they can operate under all lighting conditions. This study compared the potential of active and passive canopy
sensors for predicting biomass production in 25–32 randomly selected positions of a Merlot vineyard. Both sensors provided
estimates of the normalized difference vegetation index (NDVI) from a nadir view of the canopy at veraison that were good
predictors of pruning weight. Although the red NDVI of the passive sensors explained more of the variation in biomass (R
2 = 0.82), its relationship to pruning weight was nonlinear and was best described by a quadratic regression (NDVI = 0.55 + 0.50 wt−0.21 wt2). The theoretically greater linearity of the amber NDVI-biomass relationship could not be verified under conditions of high
biomass. The linear correlation to stable isotope content in leaves (13C and 15N) provided evidence that canopy reflectance detected plant stresses as a result of water shortage and limited fertilizer
N uptake. Thus, the canopy reflectance data provided by these mobile sensors can be used to improve site-specific management
practices of vineyards. 相似文献
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Summary The amount of P- and K-application to the seed-potato crop did not show any influence on the chemical composition of the immature
harvested tubers, nor on the productivity if used as seed. Nitrogen had a marked influence on the chemical composition of
the tubers.
Seed from plots with high nitrogen dressing showed a tendency to give fewer main stems. Concerning the productivity of the
seed the experiments showed contradictory results. It is concluded that the amount of fertilizer applied to the seed-potato
crop is of little importance for the productivity of the progeny.
Retired in 1965. 相似文献
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Fitness of isolates of Sphaerotheca fuliginea resistant or sensitive to fungicides which inhibit ergosterol biosynthesis 总被引：3，自引：0，他引：3
H. T. A. M. Schepers 《European journal of plant pathology / European Foundation for Plant Pathology》1985,91(2):65-76
Isolates ofSphaerotheca fuliginea resistant to fungicides which inhibit ergosterol biosynthesis (EBIs: bitertanol, fenarimol, imazalil) had been collected from glasshouses in the Netherlands. Fitness of these isolates was compared to that of isolates with a wild-type sensitivity to EBIs. Fitness parameters studied were germination of conidia, growth of germ tubes and mycelium, penetration, sporulation and competitive ability.In an experiment in which 10 EBI-resistant isolates were compared to 7 wild-type isolates, one or more values of fitness parameters for EBI-resistant isolates were slightly lower than those for the wild-type isolates. However, within the group of resistant isolates no relation existed between the degree of resistance to EBIs and the degree of fitness. In an experiment with fewer isolates but with more replicates, differences in fitness between EBI-resistant and wild-type isolates were not detected over a three-month period.In competition experiments in which no crowding was present, resistant isolates competed well with the wild-type isolate.It is concluded that the hypothesis that resistance to EBIs is unlikely to develop under practical conditions because of decreased fitness of EBI-resistant strains, does not seem to hold forS. fuliginea.Samenvatting Uit kassen in Nederland waren isolaten vanSphaerotheca fuliginea verzameld, die resistent waren tegen fungiciden die de ergosterol-biosynthese remmen (EBR's: bitertanol, fenarimol, imazalil). De fitness van deze isolaten werd vergeleken met die van isolaten met een wild-type gevoeligheid voor EBR's. De volgende fitness-parameters werden bestudeerd: sporekieming, groei van kiembuizen en mycelium, penetratie, sporulatie en competitievermogen.In een proef, waarin 10 EBR-resistente isolaten werden vergeleken met 7 wild-type isolaten, waren één of meer fitness-parameters iets lager dan die van de wild-type isolaten. Binnen de groep van de resistente isolaten bestond geen relatie tussen de mate van resistentie tegen EBR's en de waarden van de fitness-parameters. In een proef met iets minder isolaten maar met meer herhalingen in de tijd, werden geen verschillen in fitness waargenomen tussen de EBR-resistente en wild-type isolaten. In competitieproeven waarin een epidemie zich kon ontwikkelen, concurreerden de resistente isolaten goed met het wild-type isolaat.Er wordt geconcludeerd dat de hypothese dat resistentie tegen EBR's in de praktijk waarschijnlijk niet zou optreden vanwege een verminderde fitness van de EBR-resistente isolaten, niet van toepassing is opS. fuliginea. 相似文献
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C. J. T. Spitters H. J. W. Van Roermund H. G. M. G. Van Nassau J. Schepers J. Mesdag 《European journal of plant pathology / European Foundation for Plant Pathology》1990,96(1):3-15
Relations between leaf rust progress, foliage senescence and yield reduction were studied for seven winter wheat genotypes, differing in their partial resistance to leaf rust. Leaf rust accelerated leaf and ear senescence. Photosynthesis measurements showed, however, that the photosynthetic capacity of the remaining green surface was not affected. Differences between genotypes in yield reduction were largely explained by differences in leaf senescence and, therefore, in cumulative light interception (r=0.83) and crop photosynthesis. Reduction in cumulative light interception was closely related to the area under the disease-progress-curve (r=0.85), which was also closely associated with yield reduction (r=0.88). However, the time taken to reach a 50% reduction of green leaf area and the pustule density on 1 July (i.e. halfway through the epidemic) were just as good predictors of yield reduction as cumulative light interception and area under disease-progress-curve, suggesting that the former are useful criteria in the selection for partial resistance to leaf rust.Samenvatting De relatie stussen de epidemiologie van bruine roest, bladveroudering en oprengstderving werden bestudeerd bij zeven wintertarwegenotypen die verschilden in partiële resistentie tegen bruine roest. Bruine roest versnelde de veroudering van blad en aar. Fotosynthesemetingen wezen echter uit dat de fotosynthesecapaciteit van het resterende groene oppervlak niet werd beïnvloed. Verschillen tussen de genotypen in opbrengstderving werden voornamelijk veroorzaakt door verschillen in bladveroudering en daarmee in cumulatieve lichtinterceptie (r=0.83) en gewasfotosynthese. De reductie in cumulatieve lichtinterceptie was nauw gerelateerd aan de cumulatieve ziektedruk (in puistdagen) (r=0.85), welke ook nauw was geassocieerd met de opbrengstderving (r=0.88). De opbrengstreductie werd echter even goed voorspeld door de tijdsduur tot 50% reductie van het groene bladoppervlak en de puistdichtheid halverwege de epidemie als door cumulatieve lichtinterceptie en cumulatieve ziektedruk, waardoor beide eerste criteria gebruikt kunnen worden in de selectie voor partiële resistentie tegen bruine roest. 相似文献
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