Quantification of biotic stresses on aerial parts of plants using Chlorophyll Fluorescence Imaging and Image Analysis

Image analysis is increasingly used in plant phenotyping. Among the various imaging techniques available for plant phenotyping, Chlorophyll Fluorescence Imaging is particularly su itable for the imaging of biotic and abiotic stresses on the aerial parts of plants. Numerous chlorophyll fluorescence parameters may be measured or calculated, but only some of them may provide useful contrasts for the quantification of a given stress on leaves. In the perspective of high throughput phenotyping of biotic stresses on plants, we developed automated procedures to identify Chlorophyll Fluorescence parameters of interest for the quantification of a given biotic stress on large image datasets. The outputs of the automated procedures enable: - the visualization of the whole dataset, by providing contact sheets for each of the chlorophyll fluorescence parameter tested. - the visualization of basic statistics : radial - plot, box - plot and Mann - Whitney tests based on the mean intensity of each parameters are provided to compare the various treatments performed. - images are clustered based on histograms associated to each images, thereby enabling the clustering of images leaves displaying leaves of si milar phytosanitary status. - the objective quantification of disease incidence on each leaf tested. The quantification can discriminate varois stages of symptom development such as necrotic tissues, wilted and chlorotic tissues, and impacted tissues that do not display any symptoms visible to the eye.

Inner necrosis in grapevine rootstock mother plants in the Cognac area (Charentes, France)

The incidence and quantification of decline-associated inner necrosis in grapevine rootstock mother plants have rarely been studied. In an experimental vineyard planted in 1991 at Saintes (Charentes), susceptibility to esca was evaluated in eleven common rootstock varieties. Fifty vines per rootstock variety were used as mother plants producing long canes which were severely pruned every year. No foliar symptoms, typical of grapevine wood diseases, were seen in field inspections conducted in the summer of 1996, 2002, 2003 and 2006. In 2007, nine trunks per variety were randomly selected and were cross-sectioned at the point of greatest diameter. All sections revealed typical esca necrosis, central and/or sector-shaped, indicating that such necrosis is very common. Every section was photographed and the percentage of necrotic area was calculated by either visual assessment or image-analysis. No significant difference was detected between these two calculating methods. Based on the mean percent necrotic area, rootstock varieties were ranked in order of susceptibility from the least susceptible, ‘1103 Paulsen’ (33%), to the most susceptible, ‘101-14 MGT’ (71%). The percent of necrotic area was correlated significantly with i) the incidence of mortality and ii) the percentage of vine sections showing white rot, a type of necrosis indicating an advanced stage of wood deterioration. This study confirmed that necrosis in grapevine wood is not always associated with foliar symptoms, but that it is related positively with grapevine mortality. Furthermore, wood necrosis in mother-plants poses a risk of disseminating associated fungi through propagation material

Valence-dependent influence of serotonin depletion on model-based choice strategy.

Human decision-making arises from both reflective and reflexive mechanisms, which underpin goal-directed and habitual behavioural control. Computationally, these two systems of behavioural control have been described by different learning algorithms, model-based and model-free learning, respectively. Here, we investigated the effect of diminished serotonin (5-hydroxytryptamine) neurotransmission using dietary tryptophan depletion (TD) in healthy volunteers on the performance of a two-stage decision-making task, which allows discrimination between model-free and model-based behavioural strategies. A novel version of the task was used, which not only examined choice balance for monetary reward but also for punishment (monetary loss). TD impaired goal-directed (model-based) behaviour in the reward condition, but promoted it under punishment. This effect on appetitive and aversive goal-directed behaviour is likely mediated by alteration of the average reward representation produced by TD, which is consistent with previous studies. Overall, the major implication of this study is that serotonin differentially affects goal-directed learning as a function of affective valence. These findings are relevant for a further understanding of psychiatric disorders associated with breakdown of goal-directed behavioural control such as obsessive-compulsive disorders or addictions.This research was funded by Wellcome Trust Grants awarded to VV (Intermediate WT Fellowship) and Programme Grant (089589/Z/09/Z) awarded to TWR, BJE, ACR, JWD and BJS. It was conducted at the Behavioural and Clinical Neuroscience Institute, which is supported by a joint award from the Medical Research Council and Wellcome Trust (G00001354). YW was supported by the Fyssen Foundation. SP is supported by Marie Curie Intra-European Fellowship (FP7-People-2012-IEF).This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/mp.2015.4