Root-mediated effects in carrot resistance to the carrot fly,Psila rosae

Advances in research on the carrot, an important root vegetable in the Apiaceae family

Carrots (Daucus carota L.), among the most important root vegetables in the Apiaceae family, are cultivated worldwide. The storage root is widely utilized due to its richness in carotenoids, anthocyanins, dietary fiber, vitamins and other nutrients. Carrot extracts, which serve as sources of antioxidants, have important functions in preventing many diseases. The biosynthesis, metabolism, and medicinal properties of carotenoids in carrots have been widely studied. Research on hormone regulation in the growth and development of carrots has also been widely performed. Recently, with the development of high-throughput sequencing technology, many efficient tools have been adopted in carrot research. A large amount of sequence data has been produced and applied to improve carrot breeding. A genome editing system based on CRISPR/Cas9 was also constructed for carrot research. In this review, we will briefly summarize the origins, genetic breeding, resistance breeding, genome editing, omics research, hormone regulation, and nutritional composition of carrots. Perspectives about future research work on carrots are also briefly provided.

Isolation, identification, and bioassay of chemicals affecting nonpreference carrot-root resistance to carrot-fly larva

Roots of the carrot cultivars Vertou L.D. (resistant) and Long Chantenay (susceptible) were subjected to detailed chemical analysis to identify extracts and compounds influencing larval host-finding (preference/non-preference) behavior and to compare concentrations of these compounds in resistant and susceptible cultivars. Vertou yielded threefold less volatile material in headspace extracts of pureed roots. Extracts of chopped root in methanol, steam, hexane, and chloroform were inactive in behavioral assays. However, ether extracts were active and their hydrocarbon and carbonyl-rich fractions contained potent attractants. The principal constituent of the carbonyl-rich fraction of each cultivar was the carotatoxin complex comprising the neurotoxin falcarinol (carotatoxin), falcarindiol, and falcarindiol monoacetate, the latter compound here reported for the first time from carrot. Falcarinol (50 and 100 μg) was active in a behavioral assay, and all three ingredients of the complex were potent electrophysiological stimuli, eliciting maximum single unit responses to source concentrations of 10 ng. Furthermore, the complex was more abundant by about 1000 μg/root in Long Chantenay. As this comprised extra amounts of 70, 862, and 110 μg of falcarinol, falcarindiol, and falcarindiol monoacetate, respectively, the observed differences seem both behaviorally and physiologically relevant. It is generally accepted that coevolution has transformed the role of many toxins into host-location cues, but this seems a relatively rare example of a neurotoxin (falcarinol) evincing, in decreased concentrations, nonpreference host resistance. This evolved response to a toxin present in large concentrations is contrasted with that totrans-2-nonenal, which paralyses and kills the larva and is present in only trace amounts in the root.

Foraging in the dark - chemically mediated host plant location by belowground insect herbivores

Root-feeding insects are key components in many terrestrial ecosystems. Like shoot-feeding insect herbivores, they exploit a range of chemical cues to locate host plants. Respiratory emissions of carbon dioxide (CO(2)) from the roots is widely reported as the main attractant, however, there is conflicting evidence about its exact role. CO(2) may act as a 'search trigger' causing insects to search more intensively for more host specific signals, or the plant may 'mask' CO(2) emissions with other root volatiles thus avoiding detection. At least 74 other compounds elicit behavioral responses in root-feeding insects, with the majority (>80 %) causing attraction. Low molecular weight compounds (e.g., alcohols, esters, and aldehydes) underpin attraction, whereas hydrocarbons tend to have repellent properties. A range of compounds act as phagostimulants (e.g., sugars) once insects feed on roots, whereas secondary metabolites often deter feeding. In contrast, some secondary metabolites usually regarded as plant defenses (e.g., dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA)), can be exploited by some root-feeding insects for host location. Insects share several host location cues with plant parasitic nematodes (CO(2), DIMBOA, glutamic acid), but some compounds (e.g., cucurbitacin A) repel nematodes while acting as phagostimulants to insects. Moreover, insect and nematode herbivory can induce exudation of compounds that may be mutually beneficial, suggesting potentially significant interactions between the two groups of herbivores. While a range of plant-derived chemicals can affect the behavior of root-feeding insects, little attempt has been made to exploit these in pest management, though this may become a more viable option with diminishing control options.