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Reducing chemical input in apple production in response to consumer and grower's environmental concerns by increasing the durability of natural disease resistance


Durable disease resistance is one of the main objectives in apple breeding. Scab (caused by the fungus Ventuna inaequalis) and powdery mildew (caused by the fungus Podosphaera leucotricha) are the two major diseases of apple; they strongly affect apple quality and yield when they are not strictly controlled by large amount of fungicides. In european orchards, chemical treatments cost 180 M.ECU per year with the overwhelming majority being for scab and mildew control (15 to 20 specific treatments per year). Such a number of treatments raises numerous ecological problems and consumer health concerns, in addition to the economic cost. Apple breeding strategies, based on monogenic resistance from wild related species, have been developed for 50 years to create new resistant varieties. Recently, many newly-created resistant varieties have been attacked by a new race of scab, showing the vulnerability of such monogenic resistance when confronted by pathogen dynamics. New ways of breeding need to be engaged in order to strenghten the already obtained resistance and to achieve durable resistance in apple: polygenic resistance should give much more durable resistance, especially if combined with monogenic resistance by using new molecular biology tools. In the same time, the risk of appearance of new fungal virulences has to be assessed.

Within this framework, miS project aims to develop plant material, a pathogen observation network, knowledge and methodologies, basic for the creation and marketing of new apple varieties carrying durable resistance against these two detrimental fungi. It is based on a close collaboration between geneticists, pathologists, breeders, pomologists and nurserymen, and involves several major objectives:
(i) characterization of new apple cultivars carrying durable disease resistance,
(ii) assessment of the risks of appearance of new virulences,
(iii) genetic dissection of polygenic resistance taking into account pathogen variability,
(iv) development of new breeding strategies,
(v) marketing analysis of several new resistant hybrids. The short-term benefits for apple growers, nurserymen and consumers will be as follows:
* identification and characterization of newly-selected hybrids carrying durable scab resistance,
* identification of traditional cultivars carrying a broad spectrum of resistance to both scab and mildew
* detection and localisation of potential new pathogen virulences in Europe (network of core orchards)
* consumer's preference assessment and marketing study on newly-selected resistant hybrids. Other practical results will be:
* construction of a core collection of V. inaequalis strains representing the pathogen variability in Europe
* characterization of the genetic bases of polygenic resistance (with molecular markers),
* identification of new resistance genes, using state-of-the-art molecular biology tools,
* selection of 'elite' genotypes combining major and minor resistance genes (marker-assisted selection)
* production of numerous new progenies combining contrasted and 'large spectrum' resistances. The complementary expertise of the different teams involved in this project (in France, the Netherlands Switzerland, Germany, Great Britain, Italy, Greece and Belgium) and the close collaboration betweer geneticists, pathologists, breeders and nurserymen are key factors for the efficient and rapid utilization of the results of this project. In addition to the economic and ecological impacts of the acquisition of durable (stable) disease resistance in apple, the accurate dissection of such host-pathogen interaction and the resulting consequences on new breeding strategies will make apple a useful model for many other fruit tree species, with potentia repercussions on their breeding strategies for durable resistance.
1. Characterisation and quantification of the oceanic influence on Atlantic-European climate Analysis of the multidecadal ensemble simulations revealed that potential decadal predictability is highest in the summer season both for tropical and extra-tropical parts of the North Atlantic European(NAE) region. In summer(winter), roughly 60% (50%) and 30% (20%) of the variance is potentially predictable for the tropical and extra-tropical parts of the NAE region respectively. There are, however, significant differences between estimates of potential predictability from different atmosphere models, particularly in spring and autumn. An optimal detection methodology was applied to the ensembles imulations to determine the space-time characteristics of the ocean icinfluence on NAE climate. It has been shown that the ocean exerts an important influence on multidecadal timescales as well as on interannual timescales. Multidecadal variations in Atlantic SST, which may be driven by the thermohaline circulation, modulate European climate. The pattern of the atmospheric response in winter has astrong projection on the North Atlantic Oscillation pattern. On interannual timescales NAE climate is influenced by ENSO but also by Atlantic SST. Notably, PREDICATE results indicate that the relative importance of these two influences is modulated by the multidecadal variation of Atlantic SST.A key finding from the idealised SST experiments is that, contrary to expectations, the response to the SST forcing is very consistent between the different atmosphere models. In many cases, the uncertainty is significantly less than the signal strength. The magnitude of the response is generally smaller than the interannual variability but is sufficient to be of clear importance for understanding and predicting decadal variability.

2. Determination of the characteristics and mechanisms of decadal variability in the Atlantic Ocean Analysis of the OGCM simulations has revealed that most of the interannual-to-decadal variability of the Atlantic Meridional Overturning Circulation (MOC) is determined by the common surface forcing. The results suggest that the strength of the MOC and associated heat transport have varied considerably over the last 50years, with a decreasing trend of 1-2Sv and 0.15 PW between 1950-1960,and a 3.5-4.5 Sv and 0.2 PW increase since 1960. This variability is caused by density anomalies in the North Atlantic subpolar gyre. The North Atlantic Oscillation plays a key role in the formation of the seanomalies by modulating air-sea fluxes in the northwest Atlantic, leading to anomalous mixing. Changes in the MOC lag changes in mixing by a few years. The ensemble simulations indicate that the evolution of the MOC can be sensitive to changes in the oceanic initial conditions. This influence is mainly seen on multidecadal timescales and appears to be linked to the salinity field in the high latitude North Atlantic. Further simulations have been used to explore sensitivity to resolution. The results show that the representation of the formation, propagation and decay of key observed, large-scale, dynamic and thermodynamic anomalies in the North Atlantic Ocean depends on model resolution, and that the major anomalies can be realistically simulated with model resolutions of 40km or less.

3. Assessments of the decadal predictability of Atlantic-European climate and development of the European capability for decadal climate forecasting The space-time structure of the simulated variability is largely consistent with the observations. In all the models the ocean icthermohaline circulation (THC) is an active player in modulating Atlantic sea surface temperatures on interdecadal timescales, and results suggest that changes in the THC have the potential to mask ananthropogenic climate signal for many decades. The mechanisms responsible for THC variability in the models have been partially understood. In all cases variations in the density of Labrador SeaWater are an important factor, but there appear to be significant differences of detail between the different models. The predictability of decadal variability has been investigated by carrying out "perfect ensemble" experiments in which the ocean icinitial conditions are assumed perfectly known, but the atmosphericinitial conditions are perturbed. The results indicate that in general the strength of the Atlantic THC is potentially predictable at least a decade in advance and, in some situations, multi-decadal predictions of the THC may be possible. In addition, THC-related variations in sea surface temperature and surface air temperature are potentially predictable one or two decades in advance. The exact level of predictability is dependent on the oceanic initial conditions and on the coupled model used.

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