Floral Scent Research Articles

Consumer Liking and Value Perception of Mountain Cheese from Different Pasture Periods: Evidence for Mountain Systems Supporting Policies

Every year, mountain pastures show a progressive impoverishment of forage. The loss in grassland feed value restricts the production period of local Pecorino cheeses, which strongly depend on the vegetative cycle of the pasture linked to climatic conditions. The Monte Fietone mountain area (Macerata, Italy) has emblematic pasture flora during spring and early summer. This unique environment is normally used for rearing sheep, allowing regular production of local Pecorino cheeses from their milk, which is rich in vitamins and intrinsic floral aromas. Biologists and agronomists are giving increasing importance to these mountain food products. We conducted sensorial tests and experimental auctions to investigate recognition of the quality of this rare artisanal product. The results indicate considerable potential for economic differentiation. Accordingly, we recommend useful and applicable marketing and policy actions to support the sustainability of mountain grazing systems.

Volatile metabolomics and coexpression network analyses provide insight into the formation of the characteristic cultivar aroma of oolong tea (Camellia sinensis)

Finished oolong tea products with distinctly characteristic cultivar aromas generally have higher economic value. To advance our understanding of the aromatic differences between Camellia sinensis cv. Tieguanyin (TGY) and Jinguanyin (JGY) cultivars and their underlying formation mechanism, volatile metabolomics analysis, electronic nose (EN) analysis, sensory evaluation, and RNA sequencing were performed during this study. The EN and sensorial analysis showed a significant difference in odour characteristics between the two cultivars, which featured sweet floral and fruity aromas and green floral aromas, respectively. A metabolomics analysis of tea products showed that linalool (floral, OAV = 50.6) and geraniol (rose-like and sweet, OAV = 1.9) may contribute to the characteristic aroma. The volatile determination at each stage during the oolong tea manufacturing process emphasized that the significant difference in linalool and geraniol contents in fresh leaves from the two cultivars and the increase rate were potential reasons for their characteristic aroma and suggested that the “Tanqing” treatment clarified and intensified the characteristic cultivar aroma. A linalool synthase CsLIN with the expected catalytic activity was identified by coexpression network analyses. Collectively, our work pinpoints two key aroma substances within two cultivars and elaborates on the potential cause of characteristic cultivar aroma formation.

Gas chromatography-mass spectrometry analysis of floral fragrance-related compounds in scented rose (Rosa hybrida) varieties and a subsequent evaluation on the basis of the analytical hierarchy process

Scented rose (Rosa hybrida) varieties are valued as ornamentals, but they also contain volatile organic compounds (VOCs) that produce pleasant aromas. In plants, aromas are produced via metabolism during growth, and each aroma compound has a unique function. In this study, the floral aroma compounds of diverse scented rose varieties were analyzed and classified. The VOCs of different rose varieties were qualitatively and quantitatively analyzed via headspace solid-phase microextraction combined with gas chromatography and mass spectrometry. The test materials were the mature flowers of 55 scented rose varieties that were cultivated under identical conditions. Seventeen important aroma compounds were selected and an analytical hierarchy process (AHP)-based method was developed to identify the most suitable essential oil resources, aromatherapy resources, and healthcare resources. A floral fragrance evaluation model was established for the comprehensive evaluation of the scented rose varieties. The 55 varieties were classified into three grades according to their suitability for each use. ‘Soeur Emmanuelle’, ‘Wollerton Old Hall’, ‘Accademia’, and ‘Tianmidemeng’ were revealed to be suitable essential oil, aromatherapy, and healthcare resources. On the basis of their aroma compound types, the fifty-five rose varieties were divided into eight groups. The results of this study provide the theoretical basis for the classification of rose flower aromas as well as the rational use of diverse rose varieties to further develop the rose industry.

Effect of Covering Crops between Rows on the Vineyard Microclimate, Berry Composition and Wine Sensory Attributes of ‘Cabernet Sauvignon’ (Vitis vinifera L. cv.) Grapes in a Semi-Arid Climate of Northwest China

Covering crops was a commonly used viticultural technique to adjust the vineyard microclimate, thus affecting the grape and wine quality. In this two-year study, the purslane (Portulaca oleracea L.) was used to cover the lands between rows in the vineyards located in the semi-arid Northwest China, Xinjiang. Results showed that the photosynthetically active radiation around the fruit zone and the temperature with the purslane covering treatment decreased. Compared with the clean tillage, covering purslane had lower TSS and higher TA in the grape berries, while lower alcohol content and higher TA was also found in their corresponding wines. Covering purslane treatment significantly increased the contents of anthocyanin and flavonol in the grapes and wines in the year 2018, but no significant effect on flavanols was observed in the wines. Norisoprenoids, esters, and C6 alcohols in the grapes and wines were increased in the purslane covering treatment, respectively. Additionally, compared to the clean tillage, the purslane covering treatment significantly improved the sensory value of the wines, especially the floral aroma and the complexity of the wines. This study helped us to better understand the feasibility of applying covering purslane in viticulture in the semi-arid climate of Northwest China.

Odor-Pollution From Fungicides Disrupts Learning and Recognition of a Common Floral Scent in Bumblebees (Bombus impatiens)

Background and AimsBumblebees provide vital pollination services to both natural and agricultural ecosystems. Consequently their declines in species-diversity and population size over the last five decades is alarming. Direct contributors to these declines include pesticides, habitat loss, and disease. However, given that colony fitness is linked to foraging success, successful conservation requires mitigation of any anthropogenic practices that negatively impact foraging. Previous work has shown that agrochemical odor-pollution, including that of fungicides, can modulate bumblebee foraging behavior. This study investigates how odor pollution from three common fungicides (Safer® Brand Garden Fungicide II, Scotts® Lawn Fungus Control, and Reliant® Systemic Fungicide) affects Bombus impatiens’ floral-odor learning and recognition using an associative learning paradigm.MethodsThe effects of fungicide-odor pollution were tested in three ways: (1) background pollution during floral-odor learning; (2) background pollution during floral-odor recognition; and (3) point (localized) pollution during floral-odor recognition. Electroantennogram (EAG) recordings from B. impatiens confirmed the salience of all odor-stimuli and examined impacts of background fungicide-odor on antennal responses to floral-odor. To better understand how fungicide-odor structure related to behavioral data, scents were sampled (Solid Phase Microextraction) and analyzed using gas chromatography–mass spectrometry. Odors were then characterized using the Compounds Without Borders (CWB) vectorization method.ConclusionAll fungicides tested disrupted floral-odor learning and recognition for at least one concentration tested, and Scotts® was universally disruptive at all tested concentrations. All fungicides induced EAG responses, indicating they provide perceivable odor stimuli. Interestingly, two of three tested fungicides (Scotts® and Reliant®) inhibit antennal responses to Monarda fistulosa odor. Odor characterization supports previous findings that sulfurous scents could be disruptive to odor-driven foraging behaviors. Inability for foraging bumblebees to associate to rewarding floral odors in the presence of fungicidal odor pollution could have negative large-scale implications for colony health and reproductive fitness.

Effects of Frying Conditions on Volatile Composition and Odor Characteristics of Fried Pepper (Zanthoxylum bungeanum Maxim.) Oil.

Fried pepper (Zanthoxylum bungeanum Maxim.) oil (FPO) is widely used in Chinese cuisine because of its unique aroma. To investigate the effects of different frying temperatures and different frying times on the volatile composition and odor characteristics of FPOs, descriptive sensory analysis (DSA), solvent-assisted flavor evaporation–gas chromatography–mass spectrometry (SAFE–GC–MS) and electronic nose (E-nose) were used to analyze the FPOs (FPO1–FPO4 represented the pepper oil fried at 110 °C, 120 °C, 130 °C, and 140 °C; FPO5–FPO7 represented the pepper oil fried for 10 min, 20 min and 30 min). The results showed that FPO3 and FPO6 had strong citrus-like and floral aromas and exhibited significant advantages in sensory attributes. A total of 46 volatile compounds were identified by SAFE–GC–MS; among them, FPO3 and FPO6 had a higher volatile compound content. β-Caryophyllene was detected in only FPO3 and FPO6; linalool was higher in FPO3 and FPO6, which might cause them to exhibit stronger floral and citrus-like aromas. The presence of (2E,4E)-2,4-decanedienal would be one of the reasons for the strong fatty aroma exhibited in FPO4 and FPO7. FPO3 and FPO6 were associated with citrus-like and floral aromas by partial least squares regression (PLSR) analysis, which agreed with the sensory evaluation results.

Biochemical, Sensory, and Molecular Evaluation of Flavour and Consumer Acceptability in Australian Papaya (Carica papaya L.) Varieties.

Inconsistency in flavour is one of the major challenges to the Australian papaya industry. However, objectively measurable standards of the compound profiles that provide preferable taste and aroma, together with consumer acceptability, have not been set. In this study, three red-flesh papayas (i.e., ‘RB1’, ‘RB4’, and ‘Skybury’) and two yellow-flesh papayas (i.e., ‘1B’ and ‘H13’) were presented to a trained sensory panel and a consumer panel to assess sensory profiles and liking. The papaya samples were also examined for sugar components, total soluble solids, and 14 selected volatile compounds. Additionally, the expression patterns of 10 genes related to sweetness and volatile metabolism were assessed. In general, red papaya varieties had higher sugar content and tasted sweeter than yellow varieties, while yellow varieties had higher concentrations of citrus floral aroma volatiles and higher aroma intensity. Higher concentrations of glucose, linalool oxide, and terpinolene were significantly associated with decreased consumer liking. Significant differences were observed in the expression profiles of all the genes assessed among the selected papaya varieties. Of these, cpGPT2 and cpBGLU31 were positively correlated to glucose production and were expressed significantly higher in ‘1B’ than in ‘RB1’ or ‘Skybury’. These findings will assist in the strategic selective breeding for papaya to better match consumer and, hence, market demand.

Comparative Analysis of the Floral Fragrance Compounds of Panax notoginseng Flowers under the Panax notoginseng-pinus Agroforestry System Using SPME-GC-MS.

Panax notoginseng is a medicinal plant in China, the flowers of which have high medicinal value. To study the differences in the floral fragrance compounds of P. notoginseng flowers (bionic wild cultivation) from the forests of Yunnan Province, the floral fragrance compounds from four varieties of P. notoginseng flowers (four-forked seven leaves, three-forked seven leaves, four-forked five–seven leaves, and three-forked five–six leaves) were compared and analyzed via headspace solid phase microextraction combined with gas chromatography–mass spectrometry methods. A total of 53 floral fragrance compounds from the P. notoginseng flowers were divided into eight categories, mainly consisting of terpenes, alkynes, aromatic hydrocarbons, and alcohols. Moreover, high contents of 3-carene, germacrene D, (−)-α-gurjunene, valencene, (+)-γ-gurjunene, menogene, and aromandendrene were identified from the flowers of different P. notoginseng varieties. Interestingly, floral fragrance compounds such as 3-carene, valencene, aromandendrene, menogene, and (+)-γ-gurjunene were first reported in the flowers of P. notoginseng. Cluster analysis showed that P. notoginseng with four-forked and three-forked leaves clustered into two subgroups, respectively. In addition, principal component analysis showed that (+)-γ-gurjunene, (+)-calarene, copaene, 1,8,12-bisabolatriene, γ-elemene, (–)-aristolene, caryophyllene, 3-carenes, and 2,6-dimethyl-1,3,6-heptatriene can be used to distinguish the floral fragrance components of four P. notoginseng flower species. This study provides a theoretical basis for elucidating the floral fragrance compounds emitted from the flowers of different P. notoginseng varieties in an agroforestry system.

The impact of digital scents on behavioral health in a restorative virtual reality environment

Astronauts on long-duration missions are at an increased risk of developing adverse behavioral conditions due to prolonged periods in isolated, confined, and extreme (ICE) environments. Sleep loss, sensory deprivation and monotony, and loss in social connectedness can further exacerbate their conditions and decrement performance, thus jeopardizing mission success. Future missions will require crews to travel distances that make current countermeasures increasingly difficult, as they rely on proximity to Earth. We have developed a multi-sensory virtual reality (VR) environment as a potential tool to maintain the long-term behavioral health of astronauts. We conducted a within-subjects study (N = 10) to compare the effectiveness of our VR environment with and without the incorporation of digital scents. Prior to the VR experience, subjects completed a public speaking task to elevate stress levels and emulate the stressful conditions that astronauts might encounter on a mission. The virtual nature environment features a small, forested area with localized scents that are dispersed based on the user's location in the VR environment. For example, floral scents were emitted when the user was near the field of flowers. The Positive and Negative Affect Schedule (PANAS) and the 6-item State-Trait Anxiety Inventory (STAI-6) questionnaires were administered to record subjective data on the participant's state affect and anxiety throughout the experiment. Participants reported significantly lower STAI-6 scores after the VR experience when scents were present than in the control condition (p = 0.03). Compared to the stressed state, PANAS Negative Affect (p = 0.003) and STAI-6 (p = 0.001) scores decreased after the VR with scents condition. STAI-6 scores (p = 0.013) also decreased from baseline when olfactory stimuli were added. These results suggest that the addition of olfactory stimuli to the VR environment aided in reducing negative affect and state anxiety levels. In addition, our results indicate that the use of multisensory VR environments are a promising countermeasure to support behavioral health during long-duration exploration missions.

Insight into the characteristics of cider fermented by single and co-culture with Saccharomyces cerevisiae and Schizosaccharomyces pombe based on metabolomic and transcriptomic approaches

This study aimed to explore the effect of single and co-culture with Saccharomyces cerevisiae and Schizosaccharomyces pombe on the quality of cider. It was found that the interaction effect was observed in co-culture fermentation (CF) of cider with S. cerevisiae CICC 31084 and S. pombe CICC 1760. Meanwhile, aroma and taste quality of CF was significantly improved involving increase of fruity and floral aroma, which might result from the balance of esters, higher alcohols and terpenes. Moreover, the umami intensity of CF was enhanced, and the taste of sourness and astringency became weaker, which could be due to the higher content of umami amino acid and deacidification of malate. Additionally, a combined metabolic and RNA sequencing analyses revealed a clearer association between flavor quality of cider and gene expression of yeasts. Bioinformatic analysis revealed that the varying genes and metabolites were mainly involved in pathways of carbohydrate, amino acids, energy and terpenes backbone metabolism. Finally, a metabolic pathway visualized the changes of significantly changed metabolites and differentially expressed genes in single and co-culture ciders. This study provided new insights into cider production and facilitated the application of co-culture fermentation technology in fruits cidermaking.

Characterization of the key aroma compounds in black teas with different aroma types by using gas chromatography electronic nose, gas chromatography-ion mobility spectrometry, and odor activity value analysis

Aroma is one of the key factors in evaluating tea quality. However, the dominant aroma components of black teas with different aroma characteristics are still unknown. In this study, the key aroma compounds in black teas with floral aroma, sweet aroma, and sweet & floral aroma were systematically characterized by the combination of gas chromatography electronic nose (GC-E-Nose), gas chromatography-ion mobility spectrometry (GC-IMS), and odor activity value (OAV) analysis. A satisfactory discrimination was obtained by using partial least squares-discriminant analysis, based on the volatile fingerprints from the GC-E-Nose and GC-IMS, with robustness model parameters (R2Y = 0.981, and Q2 = 0.967) and (R2Y = 0.893, and Q2 = 0.86), respectively. Among the 38 identified aroma compounds, 15 volatiles were simultaneously identified as important odorants with OAVs greater than 1 in three fragrant black teas, namely (E)-2-nonenal, linalool, nonanal, benzene acetaldehyde, octanal, benzaldehyde, oct-1-en-3-ol, heptanal, ethyl 2-methylpentanoate, (E)-2-hexen-1-ol, hexanal, 2-methylbutanal, 3-methylbutanal, (E)-3-penten-2-one, and butanal, with ethyl 2-methylpentanoate (176.44≤OAV≤1453.47), 3-methylbutanal (19.59≤OAV≤76.16), (E)-2-nonenal (37.43≤OAV≤56.46) and linalool (3.29≤OAV≤56.72) being the most notable. The results provide a theoretical support for flavor quality improvement and oriented processing of black tea.

Rodent responses to volatile compounds provide insights into the function of floral scent in mammal-pollinated plants.

Flowers pollinated by mammals have evolved in many plant families. Several scent compounds that attract bats to flowers have been identified, but the chemical ecology of pollination mutualisms between plants and ground-dwelling mammals is poorly understood. Rodents are key pollinators in South Africa and rely heavily on olfaction to locate food. Our aim was to identify compounds that may function to attract rodents to flowers. Eighteen volatile compounds, including 14 that are prominent in the scent of rodent-pollinated flowers, were used in choice experiments involving wild-caught individuals of four native rodent species. Rodents were generally attracted to oxygenated aliphatic compounds, specifically ketones and esters, but not to some aromatic compounds common in floral scents of insect-pollinated species, nor to a sulfide compound that is attractive to bats. Associative conditioning using sugar solution as a reward had only weak effects on the attractiveness of compounds to rodents. The attractive effect of some compounds disappeared when they were blended with compounds that did not attract rodents. We conclude that aliphatic ketones and esters are likely to play a key role in attracting rodents to flowers. Deployment of these compounds may allow plants to exploit rodent sensory bias that evolved in other contexts such as intra-specific communication and searching for seeds. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Generation of intra- and interspecific Saccharomyces hybrids with improved oenological and aromatic properties.

SummaryNon‐wine yeasts could enhance the aroma and organoleptic profile of wines. However, compared to wine strains, they have specific intolerances to winemaking conditions. To solve this problem, we generated intra‐ and interspecific hybrids using a non‐GMO technique (rare‐mating) in which non‐wine strains of S. uvarum, S. kudriavzevii and S. cerevisiae species were crossed with a wine S. cerevisiae yeast. The hybrid that inherited the wine yeast mitochondrial showed better fermentation capacities, whereas hybrids carrying the non‐wine strain mitotype reduced ethanol levels and increased glycerol, 2,3‐butanediol and organic acid production. Moreover, all the hybrids produced several fruity and floral aromas compared to the wine yeast: β‐phenylethyl acetate, isobutyl acetate, γ‐octalactone, ethyl cinnamate in both varietal wines. Sc × Sk crosses produced three‐ to sixfold higher polyfunctional mercaptans, 4‐mercapto‐4‐methylpentan‐2‐one (4MMP) and 3‐mercaptohexanol (3MH). We proposed that the exceptional 3MH release observed in an S. cerevisiae × S. kudriavzevii hybrid was due to the cleavage of the non‐volatile glutathione precursor (Glt‐3MH) to detoxify the cell from the presence of methylglyoxal, a compound related to the high glycerol yield reached by this hybrid. In conclusion, hybrid generation allows us to obtain aromatically improved yeasts concerning their wine parent. In addition, they reduced ethanol and increased organic acids yields, which counteracts climate change effect on grapes.

Identification of Key Aroma Compounds Responsible for the Floral Ascents of Green and Black Teas from Different Tea Cultivars.

Chemicals underlying the floral aroma of dry teas needs multi-dimensional investigations. Green, black, and freeze-dried tea samples were produced from five tea cultivars, and only ‘Chunyu2’ and ‘Jinguanyin’ dry teas had floral scents. ‘Chunyu2’ green tea contained the highest content of total volatiles (134.75 μg/g) among green tea samples, while ‘Jinguanyin’ black tea contained the highest content of total volatiles (1908.05 μg/g) among black tea samples. The principal component analysis study showed that ‘Chunyu2’ and ‘Jinguanyin’ green teas and ‘Chunyu2’ black tea were characterized by the abundant presence of certain alcohols with floral aroma, while ‘Jinguanyin’ black tea was discriminated due to the high levels of certain alcohols, esters, and aldehydes. A total of 27 shared volatiles were present in different tea samples, and the contents of 7 floral odorants in dry teas had correlations with those in fresh tea leaves (p < 0.05). Thus, the tea cultivar is crucial to the floral scent of dry tea, and these seven volatiles could be promising breeding indices.

Comparative analysis of floral scent profiles between two Chimonanthus praecox plants under different rhythms and blooming stages

Chimonanthus praecox is an economically important ornamental plant species native to China. It is known for its winter-season flowering times and strong fragrances. Floral fragrances vary with different circadian rhythms. Despite many studies examining the circadian-rhythm-based changes in floral fragrance, limited information is available about the floral fragrance of C. praecox with circadian rhythms. In this study, headspace solid-phase microextraction gas chromatography—mass spectrometry was used to identify the floral scent compounds in var. grandiflorus and var. intermedius from Yunnan, China. In total, 69 volatile compounds, which were largely acids, alcohols, esters, aromatic compounds, terpenes, aldehydes, and ketones, were identified and the most predominant compounds were alcohols. Compounds m-xylene, p-xylene, 2-norbornanemethanol, o-xylene, cyclohepta-1,3,5-triene, germacrene D, ethylbenzene and 3,4-dimethoxycinnamic acid contributed to the floral scent of C. praecox. While var. grandiflorus and var. intermedius flowers contained about the same number of floral scent compounds (53 and 52, respectively), their compositions varied greatly. Furthermore, hierarchical cluster analysis based on the main compounds in var. grandiflorus and var. intermedius with different circadian rhythms indicated that opened flowers had similar compounds while unopened flowers had different ones. In addition, the amounts and contents of floral scent compounds between the two C. praecox varieties were affected differently by temperature, humidity and light intensity. Our findings will contribute to the exploration of the biosynthesis and emission mechanisms of floral scent compounds in C. praecox.

Real-Time Visualization of Scent Accumulation Reveals the Frequency of Floral Scent Emissions.

Flowers emit a bouquet of volatiles to attract pollinators or to protect flowers from pathogen and herbivore attacks. Most floral volatiles are synthesized in the cytoplasm of petals and released into the headspace at a specific time of day. Various floral scent sampling methods coupled with gas chromatography-mass spectrometry have been used to measure the quality and quantity of floral volatiles. However, little is known about the emission patterns of floral scents. In most cases, it is still unclear whether floral scents emit continuously or discontinuously. Here we measured the frequency with which lily flowers emit scents using optical interferometry. By analyzing the refractive index difference between volatile organic compounds and ambient air, we were able to visualize the accumulation of the volatile vapors. The frequency of volatile emission was calculated from the unique footprint of temporal power spectrum maps. Based on these real-time measurements, we found that lily flowers emit the volatile compounds discontinuously, with pulses observed around every 10–50 min.

Impact of Chronic Exposure to Two Neonicotinoids on Honey Bee Antennal Responses to Flower Volatiles and Pheromonal Compounds.

Volatile compounds provide important olfactory cues for honey bees (Apis mellifera L.), which are essential for their ecology, behavior, and social communication. In the external environment bees locate food sources by the use of floral scents, while inside the hive, pheromones such as the queen mandibular pheromone (QMP) and alarm pheromones serve important functions in regulating colony life and inducing aggressive responses against intruders and parasites. Widely reported alterations of various behaviors in- and outside the hive following exposure to pesticides could therefore be associated with a disturbance of odor sensitivity. In the present study, we tested the effects of neonicotinoid pesticides at field concentrations on the ability of honey bees to perceive volatiles at the very periphery of the olfactory system. Bee colonies were subjected to treatments during the summer with either Imidacloprid or Thiacloprid at sublethal concentrations. Antennal responses to apple (Malus domestica L.) flower volatiles were studied by GC-coupled electro-antennographic detection (GC-EAD), and a range of volatiles, a substitute of the QMP, and the alarm pheromone 2-heptanone were tested by electroantennography (EAG). Short-term and long-term effects of the neonicotinoid treatments were investigated on bees collected in the autumn and again in the following spring. Treatment with Thiacloprid induced changes in antennal responses to specific flower VOCs, with differing short- and long-term effects. In the short term, increased antennal responses were observed for benzyl-alcohol and 1-hexanol, which are common flower volatiles but also constituents of the honey bee sting gland secretions. The treatment with Thiacloprid also affected antennal responses to the QMP and the mandibular alarm pheromone 2-heptanone. In the short term, a faster signal degeneration of the response signal to the positive control citral was recorded in the antennae of bees exposed to Thiacloprid or Imidacloprid. Finally, we observed season-related differences in the antennal responses to multiple VOCs. Altogether, our results suggest that volatile-specific alterations of antennal responses may contribute to explaining several behavioral changes previously observed in neonicotinoid-exposed bees. Treatment effects were generally more prominent in the short term, suggesting that adverse effects of neonicotinoid exposure may not persist across generations.

Floral volatiles may influence honey bee visitations in oilseed Brassica species

ABSTRACT Understanding foraging preferences of honey bees (Apis mellifera L.) is essential to maneuver pollinator movement to enhance outcrossing and hence the crop yields. In this communication, we report the role of floral volatile organic compounds (VOCs) in structuring foraging decisions of honey bees. Supercritical fluid extraction of VOCs, coupled with gas chromatography-mass spectrometry, revealed 75 VOCs. Of these, 19 were strong attractants and 8 were strong repellants. Moreover, we detected significant, but variable, species- or genome-level differences in floral scents. Honey bees avoided Brassica juncea cv. PBR357 (0.81 bee visits/sq m/min) and B. carinata cv. PC5 (0.77 bee visits/sq m/min), which possessed peak concentrations of antifeedants or repellents (dibutyl phthalate and 9-octadecenoic acid) in their floral volatiles. B. napus cvs. GSC6 and GSC7 attracted the highest number of bee visitations (1.07 and 0.99 bee visits/sq m/min, respectively), as these possessed VOCs with honey-fruity odor in high amounts and negligible levels of antifeedants. Our results highlight that variability in floral reward chemistry should be considered when breeding crops that are frequently visited upon by bee pollinators to support bee pollinators, in general, and honey industry, in particular.

Functional Differentiation of Floral Color and Scent in Gall Midge Pollination: A Study of a Schisandraceae Plant.

Gall midges are among the most host-specific insects. Their interactions with plants likely date back to the Cretaceous period. Plants from at least seven families are involved in gall midge pollination; however, little is known about the pollination signals of gall midges. In this study, we used a Resseliella–Schisandra model to investigate the roles of floral scent and color in attracting gall midges. Field observations, behavioral bioassays via Y-tubes, and “flight box” experiments were performed. The results demonstrated that gall midges may be attracted by both floral scent and color and that two flower signals are more effective in promoting insect flower-landing than either alone. In the field, gall midges visited male flowers effectively at night but almost always visited female flowers during the day. Thus, during the Resseliella–Schisandra interactions, female flowers predominantly employed visual cues over scent to attract midges during the day; in contrast, olfactory cues were more functional for male flowers to export pollen in the dark. In this study, we first identified the roles of floral color and the functional differentiation of visual and olfactory cues during gall midge pollination.

Evolutionary breakdown of distyly to homostyly is accompanied by reductions of floral scent inPrimula oreodoxa

AbstractReproductive traits that function in pollinator attraction may be reduced or lost during evolutionary transitions from outcrossing to selfing. Although floral scent plays an important role in attracting pollinators in outcrossing species, few studies have investigated associations between floral scent variation and intraspecific mating system transitions. The breakdown of distyly to homostyly represents a classic example of a shift from outcrossing to selfing and provides an opportunity to test whether floral fragrances have become reduced and/or changed in composition with increased selfing. Here, we evaluate this hypothesis by quantifying floral volatiles using gas chromatography‐mass spectrometry in two distylous and four homostylous populations ofPrimula oreodoxaFranchet, a perennial herb from SW China. Our analysis revealed significant variation of volatile organic compounds (VOCs) among populations ofP. oreodoxa. Although there was no difference in VOCs between floral morphs in distylous populations as predicted, we detected a substantial reduction in VOC emissions and the average number of scent compounds in homostylous compared with distylous populations. A total of 12 compounds, mainly monoterpenoids and sesquiterpenoids, distinguished homostylous and distylous morphs; of these, (E)‐β‐ocimene was the most important in contributing to the difference in volatiles, with significantly lower emissions in homostyles. Our findings support the hypothesis that the transition from outcrossing to selfing is accompanied by the loss of floral volatiles. The modification to floral fragrances inP. oreodoxaassociated with mating system change might occur because high selfing rates in homostylous populations result in relaxed selection for floral attractiveness.