1,148 research outputs found
Response of 'Merlot' (Vitis vinifera) grapevine to defoliation caused by downy mildew (Plasmopara viticola) during the following growing season
The downy mildew (Plasmopara viticola) epidemics on leaf canopy during the ripening phase causes a stress situation for the grapevine. The plant compensates the carbohydrate request of the berries mobilising the carbohydrate reserves stored in the woody parts. In this fourth study the impact of the reserves reduction on the growth and fertility and the recovering capacity of the plant were analysed during two consecutive periods of two years (first year = stress; second year = recovering). Two treatments were compared: “Untreated canopy” (to prevent quantity losses, the clusters were treated once with a contact fungicide at the discovery of the first downy mildew sporulation) and “Standard schedule” (schedule normally applied in the vineyard). The impact of decreased reserve contents in the following growth season has negatively influenced only the shoot elongation and the potential crop yield quantity of the “Untreated canopy” treatment. Nevertheless, a single recovery year was enough to rebuild the reserve pool particularly in the roots, confirming the acclimation potential of the grapevine.
Influence of Plasmopara viticola on gas exchange parameters on field-grown Vitis vinifera 'Merlot'
The impact of downy mildew (Plasmopara viticola) epidemic on main and lateral leaf assimilation capacity of Vitis vinifera 'Merlot' has been quantified, under field conditions during the ripening phase, by means of leaf gas exchange measurements. The aim was to describe the impact of different disease severity levels on the gas exchange rate of symptomless portions of main and lateral leaves and of the sporulating parts in comparison with healthy leaves. The measurements were carried out on plants normally treated and on plants where only the clusters were treated with a contact fungicide to prevent quantity yield losses. A drastic reduction in the photosynthetic rate was observed on the sporulating area of main and lateral leaf tissues. Stomatal and mesophyll conductance decreased and stomatal resistance increased, indicating the difficulty of CO2 diffusing through the stomata into the mesophyll to the site of carboxylation. Downy mildew affected more negatively the gas exchange parameters on the symptomless parts of a diseased lateral leaf than of a main leaf, indicating a greater susceptibility of lateral leaves. A decrease of stomatal conductance and, consequently, of the photosynthetic rate, transpiration and water use efficiency was observed already at low severity level with increments of the disease severity on the leaf. At the same time an increase of stomatal resistance on the symptomless area of a lateral leaf was measured. Visual assessment of the diseased leaf area didn’t reflect the actual part colonized by the pathogen and at least a portion of the leaf area determined as healthy has in fact a latent lesion. Therefore, the visual estimation of downy mildew infection may not give a good indication of the effect of the pathogen on host physiology. The results also emphasized the important role of downy mildew as a stress element for the plant during ripening phase, a source element for carbohydrate production.
Quantification of the influence of the downy mildew (Plasmopara viticola) epidemics on the compensatory capacities of Vitis vinifera 'Merlot' to limit the qualitative yield damage
A preview study on the analysis of the impact of downy mildew (Plasmopara viticola) epidemics on the plant growth and yield quality has shown no correlation between disease severity progress on the canopy and sugar accumulation in the berries from veraison until harvest, indicating the capacity of the vine to compensate a stress situation induced by the downy mildew damage on leaf canopy. In this study the compensation capacity of the plant was analysed during three years under field conditions comparing three different downy mildew control strategies: A = “Untreated canopy” (to prevent quantity losses, the clusters were treated once with a contact fungicide at the discovery of the first downy mildew sporulation); B = “Reduced fungicide schedule” (based on a first treatment at the appearance of the first symptoms, to avoid yield quantity losses followed by one or two additional fungicide applications during the early epidemic phase with the aim of delaying the epidemic). C = “Standard schedule” (schedule normally applied in the vineyard). The experimental plot was moved each year to avoid stress influence due to a repetition of the trials on the same place. The grapevine compensated for the carbohydrate requirements of the cluster by mobilizing the starch reserves stored in the woody parts. Roots were the most important site of carbohydrate accumulation used from the grapevine and the mobilisation was higher in treatment A followed by treatment B. This compensation did not completely exhaust the reserves of each woody part and lets suppose a hierarchical pattern of the mobilisation; first a mobilisation of the reserves stored in the roots, and secondly those from the trunk, cane and shoot. The downy mildew could be considered as a stress factor for the grapevine.
Quantitative effect of leaf damage caused by downy mildew (Plasmopara viticola) on growth and yield quality of grapevine 'Merlot' (Vitis vinifera)
The impact of downy mildew (Plasmopara viticola) epidemics on the plant growth and yield quality was analysed during three years under field conditions in order to show a relationship between disease severity on leaves and yield quality losses. Three different treatments were compared: A = “Untreated canopy” (to prevent quantity losses, the clusters were treated once with a contact fungicide at the discovery of the first downy mildew sporulation); B = “Reduced fungicide schedule” (based on a first treatment at the appearance of the first symptoms, to avoid yield quantity losses followed by one or two additional fungicide applications during the early epidemic phase with the aim of delaying the epidemic). C = “Standard schedule” (schedule normally applied in the vineyard). The experimental plot was moved each year to avoid stress influence due to a repetition of the trials on the same place. The epidemic progress in the treatment A has shown the same tendency during the three years with an increase starting from the beginning of the ripening phase. The disease severity was more important on the lateral than on the main leaves. During the three years of the study, the disease did not influence the amount of total healthy leaf area per plant until veraison. From this phenological stage until harvest, the healthy leaf area per plant decreased rapidly at the same time as the epidemic increased. The yield quantity was not affected indicating that a single fungicide application at the finding of the first sporulation was enough to preserve the crop production. Among the yield quality parameters, the sugar content has been negatively influenced by the downy mildew leaf damage. The difference was particularly evident between the treatments A and C with differences from 1.4 to 2.04 °Brix. Generally, treatment B didn’t differ from C. Sugar uptake in the berries begun to show a different dynamic between 7 and 14 days after the onset of ripening. No correlation between disease severity progress on the canopy and sugar accumulation in the berries from veraison until harvest was found, indicating the capacity of the vine to compensate a stress situation induced by the downy mildew damage on leaf canopy.
Mapping quantitative physiological traits in apple ( Malus × domestica Borkh.)
Efficient breeding and selection of high-quality apple cultivars requires knowledge and understanding of the underlying genetics. The availability of genetic linkage maps constructed with molecular markers enables the detection and analysis of major genes and quantitative trait loci contributing to the quality traits of a genotype. A segregating population of the cross between the apple varieties 'sFiesta' (syn. 'sRed Pippin') and 'sDiscovery' has been observed over three years at three different sites in Switzerland and data on growth habit, blooming behaviour, juvenile period and fruit quality has been recorded. QTL analyses were performed, based on a genetic linkage map consisting of 804 molecular markers and covering all 17 apple chromosomes. With the maximum likelihood based interval mapping method, the investigated complex traits could be dissected into a number of QTLs affecting the observed characters. Genomic regions participating in the genetic control of stem diameter, plant height increment, leaf size, blooming time, blooming intensity, juvenile phase length, time of fruit maturity, number of fruit, fruit size and weight, fruit flesh firmness, sugar content and fruit acidity were identified and compared with previously mapped QTLs in apple. Although 'sDiscovery' fruit displayed a higher acid content, both acidity QTLs were attributed to the sweeter parent 'sFiesta'. This indicated homozygosity at the acidity loci in 'sDiscovery' preventing their detection in the progeny due to the lack of segregatio
Vr 2: a new apple scab resistance gene
Reports from several European countries of the breakdown of the Vf resistance, the most frequently used source of resistance in breeding programs against apple scab, emphasize the urgency of diversifying the basis of apple scab resistance and pyramiding different apple scab resistances with the use of their associated molecular markers. GMAL 2473 is an apple scab resistant selection thought to carry the resistance gene Vr. We report the identification by BSA of three AFLP markers and one RAPD marker associated with the GMAL 2473 resistance gene. SSRs associated with the resistance gene were found by (1) identifying the linkage group carrying the apple scab resistance and (2) testing the SSRs previously mapped in the same region. One such SSR, CH02c02a, mapped on linkage group 2, co-segregates with the resistance gene. GMAL 2473 was tested with molecular markers associated with other apple scab resistance genes, and accessions carrying known apple scab resistance genes were tested with the SSR linked to the resistance gene found in GMAL 2473. The results indicate that GMAL 2473 does not carry Vr, and that a new apple scab resistance gene, named Vr 2, has been identifie
Molecular markers linked to the apple scab resistance gene Vbj derived from Malus baccata jackii
Breeding for scab-resistant apple cultivars by pyramiding several resistance genes in the same genetic background is a promising way to control apple scab caused by the fungus Venturia inaequalis. To achieve this goal, DNA markers linked to the genes of interest are required in order to select seedlings with the desired resistance allele combinations. For several apple scab resistance genes, molecular markers are already available; but until now, none existed for the apple scab resistance gene Vbj originating from the crab apple Malus baccata jackii. Using bulk segregant analysis, three RAPD markers linked to Vbj were first identified. These markers were transformed into more reliable sequence-characterised amplified region (SCAR) markers that proved to be co-dominant. In addition, three SSR markers and one SCAR were identified by comparing homologous linkage groups of existing genetic maps. Discarding plants showing genotype-phenotype incongruence (GPI plants) plants, a linkage map was calculated. Vbj mapped between the markers CH05e03 (SSR) and T6-SCAR, at 0.6cM from CH05e03 and at 3.9cM from T6-SCAR. Without the removal of the GPI plants, Vbj was placed 15cM away from the closest markers. Problems and pitfalls due to GPI plants and the consequences for mapping the resistance gene accurately are discussed. Finally, the usefulness of co-dominant markers for pedigree analysis is also demonstrate
Controlling circular polarization of light emitted by quantum dots using chiral photonic crystal slab
We study the polarization properties of light emitted by quantum dots that
are embedded in chiral photonic crystal structures made of achiral planar GaAs
waveguides. A modification of the electromagnetic mode structure due to the
chiral grating fabricated by partial etching of the wave\-guide layer has been
shown to result in a high circular polarization degree of the quantum
dot emission in the absence of external magnetic field. The physical nature of
the phenomenon can be understood in terms of the reciprocity principle taking
into account the structural symmetry. At the resonance wavelength, the
magnitude of is predicted to exceed 98%. The experimentally achieved
value of % is smaller, which is due to the contribution of
unpolarized light scattered by grating defects, thus breaking its periodicity.
The achieved polarization degree estimated removing the unpolarized nonresonant
background from the emission spectra can be estimated to be as high as 96%,
close to the theoretical prediction
The transcription factor Hey and nuclear lamins specify and maintain cell identity
The inability of differentiated cells to maintain their identity is a hallmark of age-related diseases. We found that the transcription factor Hey supervises the identity of differentiated enterocytes (ECs) in the adult Drosophila midgut. Lineage tracing established that Hey-deficient ECs are unable to maintain their unique nuclear organization and identity. To supervise cell identity, Hey determines the expression of nuclear lamins, switching from a stem-cell lamin configuration to a differentiated lamin configuration. Moreover, continued Hey expression is required to conserve large-scale nuclear organization. During aging, Hey levels decline, and EC identity and gut homeostasis are impaired, including pathological reprograming and compromised gut integrity. These phenotypes are highly similar to those observed upon acute targeting of Hey or perturbation of lamin expression in ECs in young adults. Indeed, aging phenotypes were suppressed by continued expression of Hey in ECs, suggesting that a Hey-lamin network safeguards nuclear organization and differentiated cell identity
Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review
The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO<sub>2</sub> dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO<sub>2</sub> fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO<sub>2</sub> and the soil matrix, such as CO<sub>2</sub> diffusion and dissolution processes within the soil profile. Finally, we highlight state-of-the-art stable isotope methodologies and their latest developments. From the presented evidence we conclude that there exists a tight coupling of physical, chemical and biological processes involved in C cycling and C isotope fluxes in the plant-soil-atmosphere system. Generally, research using information from C isotopes allows an integrated view of the different processes involved. However, complex interactions among the range of processes complicate or currently impede the interpretation of isotopic signals in CO<sub>2</sub> or organic compounds at the plant and ecosystem level. This review tries to identify present knowledge gaps in correctly interpreting carbon stable isotope signals in the plant-soil-atmosphere system and how future research approaches could contribute to closing these gaps
- …