Influence of temperature on the rhythmic emission of volatiles from Ribes nigrum flowers in situ

The floral volatiles of blackcurrant (Ribes nigrum) were collected in situ using the headspace technique. Eleven compounds were identified, including monoterpenes hydrocarbons and monoterpene ethers. The fragrance was emitted in a rhythmic manner, the maximum being in the middle of the photoperiod. Emission at 20°C was significantly higher than at 10°C. The rhythmic nature of emission seemed to cease under conditions of constant light. However, a slight rise in emission during the second period in continuous light may indicate a circadian control of emission. The significance of flower volatiles in relation to pollination is discussed.     

Dynamic trajectories of volatile and non‐volatile specialised metabolites in ‘overnight’ fragrant flowers of Murraya paniculata

• Ephemeral flowers, especially nocturnal ones, usually emit characteristic scent profiles within their post‐anthesis lifespans of a few hours. Whether these flowers exhibit temporal variability in the composition and profile of volatile and non‐volatile specialised metabolites has received little attention.
• Flowers of Murraya paniculata bloom in the evenings during the summer and monsoon, and their sweet, intense fragrance enhances the plant's value as an ornamental. We aimed to investigate profiles of both volatile and non‐volatile endogenous specialised metabolites (ESM) in nocturnal ephemeral flowers of M. paniculata to examine whether any biochemically diverse groups of ESM follow distinct patterns of accumulation while maintaining synchrony with defensive physiological functions.
• Targeted ESM contents of M. paniculata flowers were profiled at ten time points at 2‐h intervals, starting from late bud stage (afternoon) up to the start of petal senescence (mid‐morning). Emitted volatiles were monitored continuously within the whole 20‐h period using headspace sampling. The ESM contents were mapped by time point to obtain a highly dynamic and biochemically diverse profile. Relative temporal patterns of ESM accumulation indicated that the active fragrance‐emitting period might be divided into ‘early bloom’, ‘mid‐bloom’ and ‘late bloom’ phases. Early and late bloom phases were characterised by high free radical generation, with immediate enhancement of antioxidant enzymes and phenolic compounds. The mid‐bloom phase was relatively stable and dedicated to maximum fragrance emission, with provision for strong terpenoid‐mediated defence against herbivores. The late bloom phase merged into senescence with the start of daylight; however, even the senescent petals continued to emit fragrance to attract diurnal pollinators.
• Our study suggests that dynamic relations between the different ESM groups regulate the short‐term requirements of floral advertisement and phytochemical defence in this ephemeral flower. This study also provided fundamental information on the temporal occurrence of emitted volatiles and internal pools of specialised metabolites in M. paniculata flowers, which could serve as an important model for pollination biology of Rutaceae, which includes many important fruit crops.

     

Response of garden chafer, Phyllopertha horticola, to plant volatiles: from screening to application

Field tests were performed on a golf course and in an apple orchard to screen synthetic plant volatiles with respect to their attractiveness for the garden chafer, Phyllopertha horticola L. (Coleoptera: Scarabaeidae), and to investigate the possible application of plant volatiles for garden chafer control. The chemicals tested were green leaf volatiles (GLV), terpenoids, and phenylpropanoids. Funnel traps baited with the GLV (Z)‐3‐hexen‐1‐ol, 1‐hexanol (Z)‐3‐hexenal, and hexanal captured more P. horticola than unbaited controls. Furthermore, traps baited with all tested floral terpenoids (i.e., geraniol, geranyl acetate, citronellol, linalool, and nerol) and phenylpropanoids (i.e., eugenol, anethol, isoeugenol, eugenyl acetate, and isoeugenyl acetate) captured more garden chafers than controls. Different dispenser types loaded once with a mixture of (Z)‐3‐hexen‐1‐ol (50%), geraniol (11.5%), eugenol (27%), and 2‐phenylethyl propionate (11.5%) attracted P. horticola over a whole flight season. A commercially available membrane dispenser had the best properties, combining the highest number of captured beetles with a low release rate. A simple modification of the trap design, i.e., a reduction of the funnel outlet diameter, significantly reduced the capture of beneficial non‐target insects (Apoidea), without influencing the number of captured garden chafers. A mass trapping experiment in the apple orchard revealed that the use of attractant traps significantly reduced the percentage of apples disfigured by feeding holes of adult garden chafers (control area: 18.9%, test area: 11.6%). The possible application of synthetic plant volatiles in mass trapping and monitoring approaches for garden chafer control is discussed.     

Three New Polyacetylene Glycosides from the Roots of Heracleum dissectum and Their Triglyceride Accumulating Activities in 3T3‐L1 Cells

Continually phytochemical study of the roots of Heracleum dissectum had led to the isolation of three previously undescribed polyacetylene glycosides ( 1 – 3 ), together with seven known compounds, including one polyacetylene ( 8 ) and six coumarins ( 4 – 7 and 9 – 10 ) using diverse chromatographic methods. The structures of these three new compounds were characterized and identified as deca‐4,6‐diyn‐1‐yl β‐d ‐glucopyranosyl‐(1→6)‐β‐d ‐glucopyranosyl‐(1→2)‐β‐d ‐glucopyranoside ( 1 ), (8Z)‐dec‐8‐ene‐4,6‐diyn‐1‐yl β‐d ‐glucopyranosyl‐(1→6)‐β‐d ‐glucopyranosyl‐(1→2)‐β‐d ‐glucopyranoside ( 2 ), and (8E)‐dec‐8‐ene‐4,6‐diyn‐1‐yl β‐d ‐glucopyranosyl‐(1→6)‐β‐d ‐glucopyranosyl‐(1→2)‐β‐d ‐glucopyranoside ( 3 ) based on their physicochemical properties and extensive analyses of various spectroscopic data. Their triglycerides accumulating activities were assayed and the results showed that the three new polyacetylene glycosides ( 1 – 3 ) exhibited triglyceride accumulating activities in 3T3‐L1 adipocytes.     

Floral scent emission and pollinator attraction in two species of <Emphasis Type="Italic">Gymnadenia</Emphasis> (Orchidaceae)

We investigated scent composition and pollinator attraction in two closely related orchids, Gymnadenia conopsea (L.) R.Br. s.l. and Gymnadenia odoratissima (L.) Rich. in four populations during the day and night. We collected pollinators of both species using hand nets and sampled floral odour by headspace sorption. We analysed the samples by gas chromatography with mass spectrometry to identify compounds and with electroantennographic detection to identify compounds with physiological activity in pollinators. In order to evaluate the attractiveness of the physiologically active compounds, we carried out trapping experiments in the field with single active odour substances and mixtures thereof. By collecting insects from flowers, we caught eight pollinators of G. conopsea, which were members of four Lepidoptera families, and 37 pollinators of G. odoratissima, from five Lepidopteran families. There was no overlap in pollinator species caught from the two orchids using nets. In the scent analyses, we identified 45 volatiles in G. conopsea of which three (benzyl acetate, eugenol, benzyl benzoate) were physiologically active. In G. odoratissima, 44 volatiles were identified, of which seven were physiologically active (benzaldehyde, phenylacetaldehyde, benzyl acetate, 1-phenyl-2,3-butandione, phenylethyl acetate, eugenol, and one unknown compound). In field bioassays using a mixture of the active G. odoratissima compounds and phenylacetaldehyde alone we caught a total of 25 moths, some of which carried Gymnadenia pollinia. A blend of the active G. conopsea volatiles placed in the G. odoratissima population did not attract any pollinators. The two orchids emitted different odour bouquets during the day and night, but G. odoratissima showed greater temporal differences in odour composition, with phenylacetaldehyde showing a significant increase during the night. The species differed considerably in floral odour emission and this differentiation was stronger in the active than non-active compounds. This differentiation of the two species, especially in the emission of active compounds, appears to have evolved under selection for attraction of different suites of Lepidopteran pollinators.     

Volatile Composition Screening of Salix spp. Nectar Honey: Benzenecarboxylic Acids,Norisoprenoids, Terpenes,and Others

Salix spp. nectar honey volatiles of Croatian origin were analyzed by headspace solid‐phase microextraction (HS‐SPME) and ultrasonic solvent extraction (USE), followed by gas chromatography and mass spectrometry (GC, GC/MS). Isolated volatiles were found in the honey headspace and extracts with almost exclusive distribution of several abundant compounds (e.g., phenylacetic acid, pinocembrin, 8‐hydroxy‐4,7‐dimethylcoumarin, and 3‐hydroxy‐trans‐β‐damascone in the extracts, or safranal and lilac alcohols in the headspace). Comparison with Croatian Salix spp. honeydew honey revealed similarities regarding distribution of important shikimate pathway derivatives (e.g., high percentage of phenylacetic acid) and several norisoprenoids (α‐isophorone and 4‐oxoisophorone). On the other hand, distinct features of this honey were occurrence of compounds such as pinocembrin, 8‐hydroxy‐4,7‐dimethylcoumarin, phenylacetonitrile, norisoprenoids (major ones: 3‐hydroxy‐trans‐β‐damascenone and trans‐β‐damascone), more pronounced variability of linalool‐derived compounds, as well as the abundance of 3‐methylpropanoic acid, 3‐methylbutanoic acid, 2‐methylpentanoic acid, and 3‐methylpentan‐1‐ol.     

Volatiles from rhizomes of Rhodiola rosea L

Terpenes and aroma volatiles from rhizomes of Rhodiola rosea L. from Norway have been isolated by both steam distillation and headspace solid-phase micro-extraction coupled with gas chromatography and mass spectrometry analysis. The dried rhizomes contained 0.05% essential oil with the main chemical classes: monoterpene hydrocarbons (25.40%), monoterpene alcohols (23.61%) and straight chain aliphatic alcohols (37.54%). n-Decanol (30.38%), geraniol (12.49%) and 1,4-p-menthadien-7-ol (5.10%) were the most abundant volatiles detected in the essential oil, and a total of 86 compounds were identified in both the SD and HS-SPME samples. Geraniol was identified as the most important rose-like odour compound besides geranyl formate, geranyl acetate, benzyl alcohol and phenylethyl alcohol. Floral notes such as linalool and its oxides, nonanal, decanal, nerol and cinnamyl alcohol highlight the flowery scent of rose root rhizomes.     

Volatiles from the burnet moth Zygaena filipendulae (Lepidoptera) and associated flowers,and their involvement in mating communication

The burnet moth Zygaena filipendulae L. contains the cyanogenic glucosides linamarin and lotaustralin, which can be degraded to the volatiles hydrogen cyanide (HCN), acetone and 2‐butanone. Linamarin and lotaustralin are transferred from the male to female during mating and thus are considered to be involved in mating communication. Because volatile semiochemical cues play a major role in mating communication in many insect species, the emissions of HCN, acetone and 2‐butanone from Z. filipendulae are characterized in the present study, aiming to determine the interplay between the degradation products of cyanogenic glucosides and pheromones. The volatile emissions from Z. filipendulae and flowers inducing mating are measured using headspace solid‐phase micro‐extraction and gas chromatography‐mass spectrometry analysis. All Z. filipendulae life stages emit HCN, acetone and 2‐butanone. Virgin females show higher emissions than mated females, whereas mated males have higher emissions than virgin males. Hydrogen cyanide is only rarely detected in the course of male–female copulation. These observations indicate a role for the cyanogenic glucoside derived volatiles in female calling and male courtship behaviours, although not as a defence during copulation. Males rejected for mating by a female are accepted after injection of linamarin or lotaustralin, demonstrating that cyanogenic glucosides are also important for female assessment of the fitness of the male. Volatiles from flowers occupied during mate calling are also analyzed, and emissions from males and females result in the identification of novel putative pheromones for Z. filipendulae.     

A comparative analysis of characteristic floral scent compounds in Prunus mume and related species

In order to investigate the difference in their characteristic floral scents between Prunus mume Siebold & Zucc. and the related Prunus species, their headspace volatiles and endogenous extraction were analyzed by gas chromatography–mass spectrometry. The efficiency of substrate utilization of the flowers was studied by incubating them with different alcohol substrates. Our results indicated that benzyl acetate is a dominant compound influencing the characteristic floral scent of P. mume. An alcohol substrate concentration of 4?mmol?L^?1 and a reaction time of 2?h were constituted the reaction condition for catalysis of exogenous alcohol substrates by the flowers. Under these conditions, Prunus sibirica exhibited the highest utilization efficiency for benzyl alcohol substrate while the utilization efficiency of Prunus persica was the lowest. Comparative analysis of several alcohol substrates indicated that the flowers of the tested species had selective specificity for benzyl alcohol substrates.     

Flavanone glycosides from viscum coloratum and their inhibitory effects on osteoclast formation

Two novel flavanone glycosides, homoeriodictyol 7‐O‐β‐D ‐[6‐(3‐hydroxybutanoyl)glucopyranoside] (viscumneoside IX; 1 ) and homoeriodictyol 7‐O‐β‐D ‐[6‐(3‐hydroxybutanoyl)glucopyranosyl](1→2)‐β‐D ‐glucopyranoside (viscumneoside X; 2 ), together with four known flavanoids, 2‐homoeriodictyol 7‐O‐β‐D ‐glucopyranoside ( 3 ), viscumneoside I ( 4 ), viscumneoside III ( 5 ), and 4′,5‐dihydroxy‐3′‐methoxy‐7‐(2‐O‐α‐L ‐rhamnopyranosyl‐β‐D ‐glucopyranosyloxy)flavanone ( 6 ) were isolated from stems and leaves of Viscum coloratum. Their structures were elucidated on the basis of their NMR spectra, HR‐FAB‐MS data, and acid hydrolysis. Inhibitory effects of the four compounds 1 – 4 on the formation of osteoclast‐like multinucleated cells were investigated. As a result, all the four flavanoids showed significant inhibitory effects on the formation of osteoclast‐like multinuclear cells even at a low concentration of 2 μg/ml. The activities of 1 – 4 at such a concentration exceeded or approximated to that of elcitonin, the positive control drug at a concentration of 2 U/ml, suggesting that they may be of interest for the development of new anti‐osteoporosis drugs.     

Antiviral Activity of Faramea hyacinthina and Faramea truncata Leaves on Dengue Virus Type‐2 and Their Major Compounds

The defatted fractions of the Faramea hyacinthina and F. truncata (Rubiaceae) leaf MeOH extracts showed in vitro non‐cytotoxic and anti‐dengue virus serotype 2 (DENV2) activity in human hepatocarcinoma cell lineage (HepG2). Submitting these fractions to the developed RP‐SPE method allowed isolating the antiviral flavanone (2S)‐isosakuranetin‐7‐O‐β‐d ‐apiofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 1 ) from both species and yielded less active sub‐fractions. The new diastereoisomeric epimer pair (2S) + (2R) of 5,3′,5′‐trihydroxyflavanone‐7‐O‐β‐d ‐apiofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 2a / 2b ) from F. hyacinthina; the known narigenin‐7‐O‐β‐d ‐apiofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 3 ) from both species; rutin ( 4 ) and quercetin‐4′‐β‐d ‐O‐glucopyranosyl‐3‐O‐rutinoside ( 5 ) from F. hyacinthina, and kaempferol‐3‐O‐rutinoside ( 6 ), erythroxyloside A ( 7 ) and asperuloside ( 8 ) from F. truncata have been isolated from these sub‐fractions. Compounds 4  –  8 are reported for the first time in Faramea spp.     

Phenolic compounds from the whole plants of Gentiana rhodantha (Gentianaceae)

Gentiana rhodantha Franch. ex Hemsl. (Gentianaceae), an annual herb widely distributed in the southwest of China, has been medicinally used for the treatment of inflammation, cholecystitis, and tuberculosis by the local people of its growing areas. Chemical investigation on the whole plants led to the identification of eight new phenolic compounds, rhodanthenones A–D ( 1 – 4 , resp.), apigenin 7‐O‐glucopyranosyl‐(1→3)‐glucopyranosyl‐(1→3)‐glucopyranoside ( 5 ), 1,2‐dihydroxy‐4‐methoxybenzene 1‐O‐α‐L ‐rhamnopyranosyl‐(1→6)‐β‐D ‐glucopyranoside ( 6 ), 1,2‐dihydroxy‐4,6‐dimethoxybenzene 1‐O‐α‐L ‐rhamnopyranosyl‐(1→6)‐β‐D ‐glucopyranoside ( 7 ), and methyl 2‐O‐β‐D ‐glucopyranosyl‐2,4,6‐trihydroxybenzoate ( 8 ), together with eleven known compounds, 9 – 19 . Their structures were determined on the basis of detailed spectroscopic analyses and chemical methods. Acetylcholinesterase (AChE) inhibition and cytotoxicity tests against five human cancer cell lines showed that only rhodanthenone D ( 4 ) and mangiferin ( 12 ) exhibited 18.4 and 13.4% of AChE inhibitory effects at a concentration of 10⁻⁴ M , respectively, while compounds 1 – 5 and the known xanthones lancerin ( 11 ), mangiferin ( 12 ), and neomangiferin ( 13 ) displayed no cytotoxicity at a concentration of 40 μM .     

Antennal and behavioural responses of the spruce seed moth,Cydia strobilella,to floral volatiles of Norway spruce,Picea abies,and temporal variation in emission of active compounds

We investigated whether spruce seed moth, Cydia strobilella L. (Lepidoptera: Tortricidae, Grapholitini), one of the most damaging seed predators on Norway spruce, Picea abies (L.) H. Karst (Pinaceae), uses olfactory cues during host search. Analyses with coupled gas chromatography and electroantennography revealed that antennae of both sexes of moths responded consistently to three compounds in the headspace from female spruce flowers, i.e., α‐pinene, β‐pinene, and myrcene, but not to limonene as has been previously reported for this species. The amounts of these active volatiles released from flowers and cones of P. abies were quantified, and their diurnal and seasonal variation was monitored. The total release of the active volatiles correlated well with the diurnal and seasonal flight activity of C. strobilella as revealed by catches of males in pheromone‐baited traps. In field trapping experiments, where baits were loaded with proportions and enantiomeric ratios of α‐pinene, β‐pinene, and myrcene matching those of the female P. abies floral headspace, substantial catches of male C. strobilella were achieved, whereas few females were captured. These surprising results suggest that male C. strobilella make use of host volatiles to aid them in their search for females.     

Catabolism of l–methionine in the formation of sulfur and other volatiles in melon (Cucumis melo L.) fruit

Sulfur‐containing aroma volatiles are important contributors to the distinctive aroma of melon and other fruits. Melon cultivars and accessions differ in the content of sulfur‐containing and other volatiles. l –methionine has been postulated to serve as a precursor of these volatiles. Incubation of melon fruit cubes with ¹³C‐ and ²H‐labeled l –methionine revealed two distinct catabolic routes into volatiles. One route apparently involves the action of an l ‐methionine aminotransferase and preserves the main carbon skeleton of l ‐methionine. The second route apparently involves the action of an l ‐methionine‐γ–lyase activity, releasing methanethiol, a backbone for formation of thiol‐derived aroma volatiles. Exogenous l ‐methionine also generated non‐sulfur volatiles by further metabolism of α–ketobutyrate, a product of l ‐methionine‐γ–lyase activity. α–Ketobutyrate was further metabolized into l –isoleucine and other important melon volatiles, including non‐sulfur branched and straight‐chain esters. Cell‐free extracts derived from ripe melon fruit exhibited l ‐methionine‐γ–lyase enzymatic activity. A melon gene (CmMGL) ectopically expressed in Escherichia coli, was shown to encode a protein possessing l ‐methionine‐γ–lyase enzymatic activity. Expression of CmMGL was relatively low in early stages of melon fruit development, but increased in the flesh of ripe fruits, depending on the cultivar tested. Moreover, the levels of expression of CmMGL in recombinant inbred lines co‐segregated with the levels of sulfur‐containing aroma volatiles enriched with +1 m/z unit and postulated to be produced via this route. Our results indicate that l ‐methionine is a precursor of both sulfur and non‐sulfur aroma volatiles in melon fruit.     

New Thymoquinol Glycosides and Neuroprotective Dibenzocyclooctane Lignans from the Rattan Stems of Schisandra chinensis

Three new lignans ( 1 – 3 ), together with four new thymoquinol glycosides ( 4 – 7 ), were isolated from 70%‐EtOH extract of the rattan stems of Schisandra chinensis. The structures of 1 – 7 were elucidated by detailed spectroscopic analyses, and these new compounds were identified as pinobatol‐9‐O‐β‐d ‐glucopyranoside ( 1 ), 1,2,13,14‐tetramethoxydibenzocyclooctadiene 3,12‐O‐β‐d ‐diglucopyranoside ( 2 ), 3,7‐dihydroxy‐1,2,13,14‐tetramethoxydibenzocyclooctadiene 12‐O‐β‐d ‐glucopyranoside ( 3 ), thymoquinol 2‐O‐β‐d ‐apiofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 4 ), thymoquinol 2‐O‐α‐d ‐arabinofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 5 ), thymoquinol 5‐O‐β‐d ‐apiofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 6 ), and thymoquinol 5‐O‐α‐d ‐arabinofuranosyl‐(1→6)‐β‐d ‐glucopyranoside ( 7 ). The neuroprotective activity of 1 – 7 was evaluated on PC12 cells with neurotoxicity induced by amyloid‐beta 1 – 42 (Aβ_{1 – 42}). Compounds 2 and 3 showed protecting activity against Aβ‐induced toxicity in PC12 cells.     

Electrophysiological responses of the blue willow leaf beetle, Phratora vulgatissima, to volatiles of different Salix viminalis genotypes

Among numerous other factors, host‐plant volatiles may affect selection of food plants by herbivorous insects. The blue willow leaf beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae), is known to differentiate between willow species and genotypes. However, so far no knowledge is available on the physiological abilities of this leaf beetle to respond to willow volatiles. In this study, we recorded electroantennograms of male and female P. vulgatissima to volatiles from two Salix viminalis L. (Salicaceae) genotypes: Jorr and 78021. The headspace of these genotypes were analysed by coupled gas chromatography–mass spectrometry. In addition to known green leaf volatiles (GLV), several terpenoid components were found. Both males and females of P. vulgatissima showed strong responses to the GLVs (Z)‐3‐hexenol and (Z)‐3‐hexenyl acetate, and moderate responses to (E)‐ocimene and β‐caryophyllene. Females, but not males, also responded to R‐(+)‐limonene. This work represents a further step to identify substances relevant for the orientation of P. vulgatissima to host plants.     

Behavioural and electrophysiological responses of Triatoma dimidiata nymphs to conspecific faecal volatiles

The behavioural and electrophysiological (electroantennography) responses of the first two instars of Triatoma dimidiata (Hemiptera: Reduviidae) Latreille to fresh and dry faecal headspace volatile extracts from fifth instar conspecific nymphs and synthetic compounds were analysed in this study. Recently emerged nymphs (3–5 days) aggregated around filter paper impregnated with dry faeces and around filter paper impregnated with extracts from both fresh and dry faeces. Older first instars (10–15 days) and second instars aggregated around filter paper impregnated with fresh and dry faeces, and their respective headspace extracts. Dry faecal volatile extracts elicited the strongest antennal responses, followed by fresh faecal extracts. Gas chromatography?mass spectrometry analysis of dried faecal headspace volatiles demonstrated the presence of 12 compounds: 2‐ethyl‐1‐hexanol, 1,2,4‐trimethylbenzene, n ‐octadecane, n ‐nonadecane, n ‐eicosane, n ‐heneicosane, n ‐tricosane, n ‐pentaeicosane, n ‐hexaeicosane, n ‐octaeicosane, nonanal, and 4‐methyl quinazoline. In fresh faecal headspace extracts, only nonanal was clearly detected, although there were other trace compounds, including several unidentified sesquiterpenes. Four of the 11 compounds tested individually elicited aggregation behaviour at concentrations of 100 ng/µL and 1 µg/µL. A blend containing these four components also mediated the aggregation of nymphs. These volatiles may be valuable for developing monitoring methods and designing sensitive strategies to detect and measure T. dimidiata infestation.     

Drought stress affects response of phytopathogen vectors and their parasitoids to infection‐ and damage‐induced plant volatile cues

1. The response of a phytopathogen vector to pathogen‐induced plant volatiles was investigated, as well as the response of the phytopathogen vector's parasitoid to herbivore‐induced plant volatiles released from plants with and without drought stress. 2. These experiments were performed with Asian citrus psyllid (Diaphorina citri), vector of the plant pathogen Candidatus Liberibacter asiaticus (CLas) and its parasitoid Tamarixia radiata as models. Candidatus Liberibacter asiaticus is the presumed causal pathogen of huanglongbing (HLB), also called citrus greening disease. 3. Diaphorina citri vectors were attracted to headspace volatiles of CLas‐infected citrus plants at 95% of their water‐holding capacity (WHC); such attraction to infected plants was much lower under drought stress. Attraction of the vector to infected and non‐stressed plants was correlated with greater release of methyl salicylate (MeSA) as compared with uninfected and non‐stressed control citrus plants. Drought stress decreased MeSA release from CLas‐infected plants as compared with non‐stressed and infected plants. 4. Similarly, T. radiata was attracted to headspace volatiles released from D. citri‐infested citrus plants at 95% of their WHC. However, wasps did not show preference between headspace volatiles of psyllid‐infested and uninfested plants when they were at 35% WHC, suggesting that herbivore‐induced defences did not activate to recruit this natural enemy under drought stress. 5. Our results demonstrate that herbivore‐ and pathogen‐induced responses are environmentally dependent and do not occur systematically following damage. Drought stress affected both pathogen‐ and herbivore‐induced plant volatile release, resulting in concomitant decreases in behavioural response of both the pathogen's vector and the vector's primary parasitoid.     

Effect of leucine on aroma volatiles production from Ceratocystis fimbriata grown in liquid culture

Aroma volatiles produced by Ceratocystis fimbriata on a defined liquid synthetic medium with and without the addition of leucine were identified by gas chromatography–mass spectrometry and quantified by gas chromatography-flame ionisation detection in the liquid medium as well as in the headspace. Volatiles were extracted from the liquid by simultaneous steam distillation–solvent extraction. Ceratocystis fimbriata produced a complex set of volatile intermediary metabolites, of which ethanol was the dominant compound (92–95% of total volatiles). Low molecular weight esters, alcohols, aldehydes, ketones, alkanes, and carboxylic acids were identified in the liquid broth. Alcohols and esters were the most abundant aroma volatiles. Leucine addition effected further growth and higher volatiles production. In the headspace, ethanol and ethyl acetate accounted for 92% of total volatiles over the synthetic medium and 89% when leucine was added. Aroma perception (fruity and banana) correlated closely with liquid and headspace total volatiles.