Alternaria leaf blight, caused by the fungus Alternaria dauci, is the most damaging foliar disease of carrot. Some carrot genotypes exhibit partial resistance to this pathogen and resistance Quantitative Trait Loci (rQTL) have been identified. Co-localization of metabolic QTL and rQTL identified camphene, α-pinene, α-bisabolene, β-cubebene, caryophyllene, germacrene D and α-humulene as terpenes potentially involved in carrot resistance against ALB. By combining genomic and transcriptomic analyses, we identified, under the co-localization regions, terpene-related genes which are differentially expressed between a resistant and a susceptible carrot genotype. These genes include five terpene synthases and twenty transcription factors. In addition, significant mycelial growth inhibition was observed in the presence of α-humulene and caryophyllene.

Consumers are waiting for constant improvement of nutritional and sensorial quality of fruits and vegetables. Specialized metabolites are a priority target to improve the quality of plant products due to their nutritional and sensory attributes. Among vegetables, carrot is distinguished by its ability to accumulate a wide range of metabolites in root, including polyacetylenes, carotenoids and sugars. Therefore, carrot may be considered as a root plant model to better understand the involvement of biochemical compounds in vegetable quality. Ensuring a guaranteed content of these metabolites, considering their respective sensory and nutritional attributes, is crucial to achieve an optimal quality in carrot crops. The purpose of this work is to develop an integrative approach, including different cultivars and multi-environment trials, to grasp the respective influence of different factors in the accumulation of compounds of interest. By focusing on biochemical compounds with organoleptic and nutritional attributes, this study aims to create a typology and thus identify agronomical levers to ensure a guaranteed content of metabolites of interest in carrot crops. Beyond a better appreciation of phenotypic plasticity levels obtained by variation analyses, the identification of leading environmental factors related to key metabolites content was done using PLSr models. A sequential approach was used considering the whole crop cycle and the different development stages of carrot. This work paves the way for a better mastering of carrot quality and address recommendations for breeders and growers.

Sugars and carotenoids are recognized as key quality compounds in vegetables due to their sensory and nutritional attributes. Ensuring a guaranteed content for these compounds in carrot crop is a major challenge for producers and breeders. Widely involved in plant acclimation mechanisms, the environment significantly influences their content. A multi-environment trial over two years was used in this study to identify the environmental determinism of carotenoid and sugar accumulation. After a fine characterization of cropping places in dissecting climatic variables, pedological conditions and cultural practices, PLSr models were used for predictive purposes to determine and prioritise pedoclimatic factors and cultural practices involvement. Interestingly, distinctive patterns are observed between sugars and carotenoids. Pedoclimatic factors and cultural practices effects are similar regardless studied carotenoid, with a differential effect in accumulation according to α-branch and β-branch carotenoids. For sugar metabolism, a reverse effect of leading factors is observed depending on sugars class. Our study brings to light the overall limiting effect of some climatic factors as time exposure to low temperature or atmospheric humidity. In contrast, pedological factors were shown to enhance sugar and carotenoid content in carrot, mainly phosphorus, potassium, iron and boron. This study provides useful information for carrot producers to adapt their cultural practice depending on crop place to reach a guaranteed quality in crops. Moreover, our work paves the way for a better understanding of the mechanisms underlying the major pedoclimatic factors and cultural practices effects on the accumulation of key compounds.

Renewed consumer demand motivates the nutritional and sensory quality improvement of fruits and vegetables. Specialized metabolites being largely involved in nutritional and sensory quality of carrot, a better knowledge of their phenotypic variability is required. A metabolomic approach was used to evaluate phenotypic plasticity level of carrot commercial varieties, over three years and a wide range of cropping environments spread over several geographical areas in France. Seven groups of metabolites have been quantified by HPLC or GC methods: sugars, carotenoids, terpenes, phenolic compounds, phenylpropanoids and polyacetylenes. A large variation in root metabolic profiles was observed, in relation with environment, variety and variety by environment interaction effects in decreasing order of importance. Our results show a clear diversity structuration based on metabolite content. Polyacetylenes, β-pinene and α-carotene were identified mostly as relatively stable varietal markers, exhibiting static stability. Nevertheless, environment effect was substantial for a large part of carrot metabolic profile and various levels of phenotypic plasticity were observed depending on metabolites and varieties. A strong difference of environmental sensitivity between varieties was observed for several compounds, particularly myristicin, 6MM and D-germacrene, known to be involved in responses to biotic and abiotic stress. This work provides useful information about plasticity in the perspective of carrot breeding and production. A balance between constitutive content and environmental sensitivity for key metabolites should be reached for quality improvement in carrot and other vegetables.

Synthesized by plants, carotenoids are key pigments as photoprotective compounds in chlorophyll organs and help attract pollinators and dispersers for non-chlorophyll organs such as flowers and fruits. However, in underground organs, such as roots or tubers, their role is not clearly determined. Carotenoids also represent an important class of human health metabolites as precursors of vitamin A. The carrot root, an important vegetable consumed worldwide, contains high concentrations of carotenoids, and therefore represents an interesting model to understand the accumulation in these pigments. Several approaches were combined to understand the role of carotenoid pathway genes: plant development, evolution genetics, association genetics and impact of environmental factors. Through these various studies, several genes of the carotenoid pathway are shown to be associated with the level of carotenoid content. The findings are useful for breeding for improved varieties but also for growing of quality products. However, more studies are needed to identify the respective levels of regulation of biosynthesis genes in carrot. Regulation factors outside of the pathway still need to be identified.

Conditioned both by environment, genotype and the interaction of the genotype itself with the environment, some phenotypic plasticity lies between individuals. This phenomenon allows an adaptive potential of individuals, and may depend on various mechanisms as overdominance, epistasis, pleiotropy, gene linkage and epigenetics. Depending on studied characters, some genotypes or cultivars may be more and less plastic and, in some cases, more and less stable. Considered as powerful anti-oxidants, carotenoids have large applications in medical fields as cancer preventive compounds and precursors of vitamin A and there is an interest for guaranteed carotenoid content in crops. Even if carotenoid accumulation seems to depend on a high genetic component for climacteric fruits as tomato, there is a large effect of GxE interaction overall. Thus, the genetic determinism alone does not explain carotenoid accumulation among most vegetables. Carrot is depicted as a healthy vegetable, thanks to its ability to accumulate carotenoids at high level in roots. However a large variation is observed. In spite of a well-known carotenoid biosynthesis pathway and recent progress on the genetic control, carotenoid accumulation in an underground reserve tissue remains unclear. Regulation can occur at several scales and can result from environmental influences. This article deals with the implication of genotype by environment interaction on carotenoid accumulation and the underlying mechanisms.

Aedes albopictus is a vector of arboviruses and filarial nematodes. Originating from Asia, this mosquito has rapidly expanded its geographical distribution and colonized areas across both temperate and tropical regions. Due to the increase in insecticide resistance, the use of environmentally friendly vector control methods is encouraged worldwide. Using methods based on semiochemicals in baited traps are promising for management of mosquito populations. Interestingly, human skin microbiota was shown to generate volatile compounds that attract the mosquito species Anopheles gambiae and Aedes aegypti. Here, we investigated the composition of skin bacteria from different volunteers and the attractive potential of individual isolates to nulliparous Ae. albopictus females. We showed that three out of 16 tested isolates were more attractive and two were more repulsive. We identified dodecenol as being preferentially produced by attractive isolates and 2-methyl-1-butanol (and to a lesser extent 3-methyl-1-butanol) as being overproduced by these isolates compared with the other ones. Those bacterial volatile organic compounds represent promising candidates but further studies are needed to evaluate their potential application for baited traps improvement.