Effects of resveratrol on the ultrastructure of Botrytis cinerea conidia and biological significance in plant/pathogen interactions

Many roles have been ascribed to stilbenes, namely as antimicrobial, deterrent or repellent compounds in plants, protecting them from attacks by fungi, bacteria, nematodes or herbivores, acting both as constitutive and active defense (phytoalexin) compounds. More recently, stilbenes (especially resveratrol and its derivatives) were acclaimed for their wondrous effects and wide range of purported healing and preventive powers as cardioprotective, antitumor, neuroprotective and antioxidant agents. Although there is a huge number of works concerning the role of resveratrol in human health, reports on the antifungal activity of this compound are still scarce. This study was thus conducted in order to investigate the toxicity of resveratrol at an ultra- structural level to dormant conidia of Botrytis cinerea, the causal microorganism for gray mold. In grapevine particularly, this disease can affect all the green organs but is particularly damaging for ripening berries. Observations using transmission electron microscopy showed the occurrence of damages on conidia treated with sub-lethal doses, that is, 60 μg/mL (2.6 × 10^− 4 M) of resveratrol, a concentration usually reached in grapevine leaves and grape berries challenged by this pathogen. These results provide further data about the overall mode of action of this phytoalexin and its role in the B. cinerea/grapevine interaction.     

Evaluation of the Logan & Boyce plaque index for the study of dental plaque accumulation in dogs

The objectives of this study were to assess intra-examiner (experienced examiner) and inter-examiner agreements (experienced versus non-experienced examiners) of scores assessed with the Logan & Boyce plaque index and to evaluate whether a modification of this index, where anatomical landmarks are used for horizontal division [mod L&B-AL] and dye references are used for assessing intensity of dye (plaque thickness) [mod L&B-DR], would improve repeatability. The Logan & Boyce index was found to be inaccurate when scoring plaque coverage as it underestimated the total crown surface. The contribution of the gingival part to the total tooth score was minimized by the Logan & Boyce index compared to the mod L&B-AL/DR. Precision of global plaque scorings was significantly improved by the mod L&B-AL/DR. Intra-examiner agreement of plaque thickness and plaque coverage scorings on the gingival part of the tooth was significantly improved by the mod L&B-AL/DR. Studies evaluating plaque accumulation in dogs should therefore use the mod L&B-AL/DR rather than the Logan & Boyce index.     

Identification by PCR analysis on plasmid pEA29 of isolates of Erwinia amylovora responsible of an outbreak in Central Europe

A collection of 127 strains of Erwinia amylovora, the causative agent of fire blight, was tested by PCR amplification of a fragment of the plasmid pEA29. A variability in the length of the DNA fragment obtained was observed after digestion by MspI and Sau3A restriction enzymes. Strains were distributed into three groups according to the length of the DNA product. Most of the strains analysed were placed into two groups. Thirteen strains were clustered into a third group which was linked with the geographical origin of strains: they were all isolates from recently reported outbreaks of fire blight in Austria and in southern Bavaria in Germany. The variation in the length of the amplified fragment is probably due to an insertion into this fragment.     

Pathogenic and Genetic Diversity of Soilborne Isolates of Cylindrocladium from Banana Cropping Systems

Pathogenicity and genetic variation were investigated within a collection of 104 banana-infecting isolates of Cylindrocladium (teleomorph Calonectria) originating from different countries and representing previously described morphological taxa or species. These root-rot fungi, along with endoparasitic nematodes, have been reported to be causal agents of necrotic lesions that induce root breakage and toppling of banana plants. Little is known about the individual pathogenic effects of the species involved or their genetic diversity. In the present study, among the five morphological taxa found in the banana rhizosphere, only isolates showing an atypical morphology relative to Cylindrocladium gracile (named Cy. gracile-like isolates) and Cy. spathiphylli isolates were pathogenic on banana cultivar Grande Naine. When comparing the latter isolates with others of the same species, but originating from different hosts, an analysis of rDNA spacer polymorphism partitioned isolates of Cy. spathiphylli by host into a banana – tea group and a Heliconia – Spathiphyllum group. Furthermore, isolates from Heliconia were not pathogenic on banana. A pathogenicity assessment of representative isolates from the Cy. gracile-like and the Cy. spathiphylli taxa on six different banana cultivars yielded no evidence of differential interactions between isolates and banana genotypes. Significant differences in susceptibility between banana genotypes were nevertheless detected that could potentially be exploited by breeders. Random amplified polymorphic DNA analysis revealed a genetic similarity ranging from 70% to 100% within Cy. spathiphylli isolates from bananas regardless of the geographic origin. Moreover, Cy. gracile-like isolates were highly similar but showed only 60% similarity relative to the Cy. gracile reference isolates, thus raising questions about their species status.     

Study of Bacterial Determinants Involved in the Induction of Systemic Resistance in Bean by Pseudomonas putida BTP1

The ability of Pseudomonas putida BTP1 to induce resistance in bean to Botrytis cinerea was demonstrated in soil experiments on plants pre-inoculated at the root level with the bacteria before challenge with the leaf pathogen. As a first step to characterize the molecules from BTP1 responsible for induction of systemic resistance in bean, heat-killed cells and supernatant from culture in an iron-limited medium were tested for their protective effect. Most of the resistance-eliciting activity of the strain was retained in the crude cell-free culture fluid. In vivo assays with samples from successive fractionation steps of the BTP1 supernatant led, (i) to the conclusion that salicylic acid, pyochelin and pyoverdin, previously identified as Pseudomonas determinants for induced systemic resistance (ISR), were not involved in systemic resistance triggered by BTP1, and (ii) to the isolation of fractions containing one main metabolite that retained most of the resistance-inducing activity in bean. Although this molecule remains to be structurally characterized, its isolation is an addition to the range of determinants from plant growth-promoting rhizobacteria (PGPR) known to stimulate plant defences.     

Metabolism of phenyl-3 H-indoles by cell suspension of Acer pseudoplatanus L. and their phytotoxicity

Phenyl-3H-indoles inhibited growth of Acer pseudoplatanus cells but were not toxic in vivo. Experiments were conducted to find out why the compounds gave a toxic response in cell suspension but not a phytotoxic response in whole plants. The behaviour of two phenyl-3H-indoles, (2-(4-chlorophenyl)-3,3-dimethyl-5-fluoro-3H-indole and 2-(4-chlorophenyl)-3,3-dimethyl-5-carboxy-3H-indole), was investigated in cell suspensions. Absorption and metabolism by cells were rapid. The major metabolite was identified as a polar conjugate of 2-(3-hydroxy-4-chlorophenyl)-3,3-dimethyl-5-fluoro-3H-indole. This metabolite did not inhibit cell growth. Different phenyl 3H-indole analogues with the hydroxylation site blocked were synthesised to determine if metabolism was involved in the disappearance of activity in vivo. The results indicated that this was not the case and thus the absence of phytotoxicity must be related to another factor.     

Brachypodium as a model system for grass research

The combination of a tractable experimental system, molecular tools, facile genetics and comprehensive genomics resources places Brachypodium distachyon in a unique position to promote and accelerate biological investigations in cereal and grass crops. Brachypodium has a proven track-record as a bridge into Triticeae cereal crops by helping to navigate and assemble their large and complex genomes. Brachypodium’s compact genome already provides a useful reference for map-based cloning and comparative genomics. In this review, I argue that Brachypodium will also fulfill a more generic role as a functional genomics model. In this context, Brachypodium will play a pivotal role in multi-system approaches to underpin tomorrow’s grass research landscape.     

Effects of <Emphasis Type="Italic">Inga densiflora</Emphasis> on the microclimate of coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.) and overall biomass under optimal growing conditions in Costa Rica

The advantages of associating shade trees in coffee agroforestry systems (AFS) are generally thought to be restricted mostly to poor soil and sub-optimal ecological conditions for coffee cultivation whereas their role in optimal conditions remains controversial. Thus, the objective of this study was to investigate, under the optimal coffee cultivation conditions of the Central Valley of Costa Rica, the impact of Inga densiflora, a very common shade tree in Central America, on the microclimate, yield and vegetative development of shaded coffee in comparison to coffee monoculture (MC). Maximum temperature of shaded coffee leaves was reduced by up to 5°C relative to coffee leaf temperature in MC. The minimum air temperature at night was 0.5°C higher in AFS than air temperature in MC demonstrating the buffering effects of shade trees. As judged by the lower relative extractable water (REW) in the deep soil layers during the dry season, water use in AFS was higher than in MC. Nevertheless, competition for water between coffee and associated trees was assumed to be limited as REW in the 0–150 cm soil layer was always higher than 0.3 in shaded coffee compared to 0.4 in monoculture. Coffee production was quite similar in both systems during the establishment of shade trees, however a yield decrease of 30% was observed in AFS compared to MC with a decrease in radiation transmittance to less than 40% during the latter years in the absence of an adequate shade tree pruning. As a result of the high contribution (60%) of shade trees to overall biomass, permanent aerial biomass accumulation in AFS amounted to two times the biomass accumulated in MC after 7 years. Thus provided an adequate pruning, Inga-shaded plantations appeared more advantageous than MC in optimal conditions, especially considering the fact that coffee AFS provides high quality coffee, farmers’ revenue diversification and environmental benefits.     

SIMBA,a model for designing sustainable banana-based cropping systems

Banana monocultures (Musa spp., AAA, Cavendish sub-group cv. Grande Naine) can have a detrimental impact on the environment. In these agro-systems, pesticide treatments can lead to surface and groundwater pollution, as is the case in the tropical insular conditions of the French West Indies. Using models to design alternative cropping systems is of growing interest but most of the research work has been concentrated on annual crops and most often in temperate climate. A specific model called SIMBA was built to assess environmental risks under a large range of cropping techniques and to help design more sustainable cropping systems. SIMBA simulates banana-cropping systems at field level over several cropping cycles. It includes sub-models that simulate soil structure, water balance, root nematode populations, yield, and economic outputs with a sound balance between representing the major phenomena well and keeping the model simple to reduce the parameterization costs in a large range of conditions. Agro-environmental indicators generated by the model make it possible to assess the major potential environmental impacts. The model has been developed and calibrated in Guadeloupe and Martinique and is used to draw up practical recommendations for farmers and for virtual experiments of agro-technological innovations or field management strategies. The structure of SIMBA is presented and a methodology is proposed for designing sustainable banana-based cropping systems using the model. SIMBA has been evaluated in a broad range of cropping systems in Guadeloupe by comparing model estimates to data collected in field experiments and surveys. Simulations lead to trends in rotation-based cropping systems characterized by systems that can be considered as intensive for profit evaluation, and combinations of frequent replanting, low nematicide application, no ploughing, and low fertilization level, for environmental evaluation. Simulations performed to optimize the replanting decision rule showed that relatively frequent replanting is good for profit while low frequency replantations (over four banana cycles) give a better environmental evaluation.