Induction of volatile organic compounds in chrysanthemum plants following infection by Rhizoctonia solani.

This study investigated the effects of Rhizoctonia solani J.G. Kühn infestation on the volatile organic compound (VOC) emissions and biochemical composition of ten cultivars of chrysanthemum (Chrysanthemum × morifolium /Ramat./ Hemsl.) to bring new insights for future disease management strategies and the development of resistant chrysanthemum cultivars. The chrysanthemum plants were propagated vegetatively and cultivated in a greenhouse under semi-controlled conditions. VOCs emitted by the plants were collected using a specialized system and analyzed by gas chromatography/mass spectrometry. Biochemical analyses of the leaves were performed, including the extraction and quantification of chlorophylls, carotenoids, and phenolic compounds. The emission of VOCs varied among the cultivars, with some cultivars producing a wider range of VOCs compared to others. The analysis of the VOC emissions from control plants revealed differences in both their quality and quantity among the tested cultivars. R. solani infection influenced the VOC emissions, with different cultivars exhibiting varying responses to the infection. Statistical analyses confirmed the significant effects of cultivar, collection time, and their interaction on the VOCs. Correlation analyses revealed positive relationships between certain pairs of VOCs. The results show significant differences in the biochemical composition among the cultivars, with variations in chlorophyll, carotenoids, and phenolic compounds content. Interestingly, R. solani soil and leaf infestation decreased the content of carotenoids in chrysanthemums. Plants subjected to soil infestation were characterized with the highest content of phenolics. This study unveils alterations in the volatile and biochemical responses of chrysanthemum plants to R. solani infestation, which can contribute to the development of strategies for disease management and the improvement of chrysanthemum cultivars with enhanced resistance to R. solani.

Unripe fruits of Litchi chinensis (Gaertn.) Sonn.: An overview of its toxicity.

Litchi (Litchi chinensis) is a widely consumed fruit that has been used in many food and health-promoting products worldwide. Litchi is a good source of nutrients including vitamin and minerals, dietary fibers, proteins, and carbohydrates. Of note, several studies have reported that the constituents of litchi fruits elicit antioxidant properties and help to maintain blood pressure, and reduce the risk of stroke and heart attack. An unclearly explained outbreak occurred in June 2019 in Muzaffarpur (Bihar), India resulted in the death of more than 150 children in a week, followed by a total of 872 cases and 176 deaths. This outbreak was associated with the consumption of Litchi fruits and the occurrence of acute encephalitis syndrome. In this high Litchi production region, a huge number of acute encephalitis syndrome cases have been registered in children in the past two decades with high mortality due to these neurological disorders linked to the consumption of litchi. While finding out the causes for this recurrent outbreak, whether or not it is caused by a virus or the phytotoxins of litchi is to be considered critical. Amongst the probable causes were observed to be methylene cyclopropyl acetic acid and hypoglycin-A found in unripe Litchi fruits which can cause hypoglycemia and as a plausible cause of AES outbreaks. This review addresses this recurrent outbreak in-depth exploring the possible causes and discusses the possible mechanisms by which phytotoxins of litchi such as hypoglycin A and methylene cyclopropylglycine which may elicit such toxic effects.

Responses of Adult Hypera rumicis L. to Synthetic Plant Volatile Blends.

The behavioral responses of Hypera rumicis L. adults to varying blends of synthetic plant volatiles (SPVs) at various concentrations in lieu of single compounds are reported for the first time. For this study, Rumex confertus plants were treated with two blends of SPVs at different quantities that act as either attractants or repellents to insects. Blend 1 (B1) consisted of five green leaf volatiles (GLVs), namely (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexenol, (E)-2-hexenol, and (Z)-3-hexen-1-yl acetate. Blend 2 (B2) contained six plant volatiles, namely (Z)-ocimene, linalool, benzyl acetate, methyl salicylate, ß-caryophyllene, and (E)-ß-farnesene. Each blend was made available in four different amounts of volatiles, corresponding to each compound being added to 50 µL of hexane in amounts of 1, 5, 25 and 125 ng. The effects of the two blends at the different concentrations on the insects were evaluated using a Y-tube olfactometer. Both sexes of the insects were found to be significantly repelled by the highest volatile levels of B1 and by two levels of B2 (25 and 125 ng). Females were also observed to be repelled using B2 with 5 ng of each volatile. Attraction was observed for both sexes only for B1 at the three lower volatile levels (1, 5 and 25 ng). In additional experiments, using only attractants, unmated females were found to be attracted to males, whereas mated females were only attracted to B1. Both unmated and mated males (previously observed in copula) were attracted only to females.

Induction of volatile organic compounds in Triticum aestivum (wheat) plants following infection by different Rhizoctonia pathogens is species specific.

The most popular means of plant protection is the chemical method, but this control is often connected with the need for repeating chemical treatments. Thus, eco-friendly strategies should be developed where, under the European Green Deal, aromatic plants and their repellent properties seem to constitute a good alternative. In earlier studies, we have shown that insect injury, bacteria infestation and pathogen infection induce plant volatile organic compounds (VOCs) emission, which can provide defensive functions to plants. In this study, Triticum aestivum L. (Poaceae) cv. 'Jenga' wheat plants were intentionally infected with one of four Rhizoctonia species (R. cerealis, R. solani, R. zeae, and R. oryzae). The soil was inoculated by the pathogens during sowing, whereas shoots were inoculated at stage BBCH 33. In greenhouse experiments, we measured VOCs from wheat 3, 7 and 11 days following stem infestation, or 42 days following soil inoculation of Rhizoctonia spp. VOC emissions were found to be largest on days 7 or 11 post-stem inoculation (>3 days post-stem inoculation >42 days post-soil inoculation). T. aestivum infected by pathogens induced five common green leaf volatiles (GLVs), namely (Z)-3-hexenal = (Z)-3-HAL, (E)-2-hexenal = (E)-2-HAL, (Z)-3-hexen-1-ol = (Z)-3- HOL, (E)-2-hexenol = (E)-2-HOL, (Z)-3-hexen-1-yl acetate = (Z)-3-HAC], six common terpenes (ß-pinene = ß-PIN, ß-myrcene = ß-MYR, Z-ocimene = Z-OCI, linalool = LIN, benzyl acetate = BAC, ß-caryophyllene = ß-CAR), and indole = IND. We found that R. cerealis infested T. aestivum emitted the largest amounts of (Z)-3-HAL and (Z)-3-HAC, while T. aestivum infested by R. solani released the largest amount of LIN (7 or 11 days following stem infestation). VOCs released by the T. aestivum after R. cerealis (AGD I) and R. solani (AG 5) infestations were significantly larger in comparison to R. zeae (WAG-Z) and R. oryzae (WAG-O) for the volatiles (Z)-3-HAL, (E)-2-HAL, (Z)-3-HOL, (E)-2-HOL, (Z)-3-HAC, ß-PIN, ß-MYR, and LIN. With the exception of (E)-2-HOL, ß-MYR, LIN, BAC, ß-CAR, the other VOCs were emitted in similar amounts by infected T. aestivum 3 days following stem and soil inoculation. The quantities of induced VOCs were higher at days 7 and 11 than at 3 days post-infection, and greater when T. aestivum was infected with Rhizoctonia on the stem base than through the soil.

Sarracenia alata (Alph.Wood) Alph.Wood Microcuttings as a Source of Volatiles Potentially Responsible for Insects' Respond.

Rare carnivorous plants representing the genus Sarracenia are perceived as very interesting to scientists involved in various fields of botany, ethnobotany, entomology, phytochemistry and others. Such high interest is caused mainly by the unique capacity of Sarracenia spp. to attract insects. Therefore, an attempt to develop a protocol for micropropagation of the Sarracenia alata (Alph.Wood) Alph.Wood, commonly named yellow trumpets, and to identify the specific chemical composition of volatile compounds of this plant in vitro and ex vivo was undertaken. Thus, the chemical volatile compounds excreted by the studied plant to attract insects were recognized with the application of the headspace solid-phase microextraction (HS-SPME) coupled with the GC-MS technique. As the major volatile compounds (Z)-3-hexen-1-ol (16.48% ± 0.31), (E)-3-hexen-1-ol acetate (19.99% ± 0.01) and ß-caryophyllene (11.30% ± 0.27) were identified. Further, both the chemical assumed to be responsible for attracting insects, i.e., pyridine (3.10% ± 0.07), and whole plants were used in in vivo bioassays with two insect species, namely Drosophila hydei and Acyrthosiphon pisum. The obtained results bring a new perspective on the possibilities of cultivating rare carnivorous plants in vitro since they are regarded as a valuable source of bioactive volatile compounds, as including ones with repellent or attractant activity.

Beetle Orientation Responses of Gastrophysa viridula and Gastrophysa polygoni (Coleoptera: Chrysomelidae) to a Blend of Synthetic Volatile Organic Compounds.

The invasive weed Rumex confertus Willd. (mossy sorrel) is eaten and severely defoliated by oligophagous Gastrophysa viridula Deg. (dock leaf beetle) and Gastrophysa polygoni L. (knotweed leaf beetle). The most popular methods of plant protection involve the application of chemicals, but such methods often require repeated chemical treatments. Aromatic plants may constitute an eco-friendly alternative strategy owing to their repellent properties. To date, single compounds have been tested rather than blends; however, there is a need to investigate mixtures of compounds, because insects are subjected to blends of odors derived from their surrounding environments. The aim of the current study was to investigate behavioral responses of the dock leaf beetle and knotweed leaf beetle to a blend of synthetic plant volatile organic compounds. Plants were treated with standard repellents (a blend of volatile organic compounds) at two different concentrations (10 ng min-1 and 1,000 ng min-1). For further experiments, four rates (1 ng min-1, 10 ng min-1, 100 ng min-1, and 1,000 ng min-1 in 50 µl) were evaluated using a 4-way olfactometer. Leaf beetles of both sexes were repelled by the highest three concentrations tested. Female dock leaf beetles were also repelled by the lowest concentration tested, where individual components could have occasionally attracted insects. These results indicate a difference in responses to individual compounds and mixtures of compounds.

Synthetic cis-jasmone exposure induces wheat and barley volatiles that repel the pest cereal leaf beetle, Oulema melanopus L.

The plant semiochemical cis-jasmone primes/induces plant resistance that deters herbivores and attracts natural enemies. We studied the induction of volatile organic compounds (VOCs) in winter wheat and spring barley after exposure of plants to three synthetic cis-jasmone doses (50 µl of 1, 100, and 1 × 10(4) ng µl(-1)) and durations of exposure (1, 3, and 6 h). Cereal leaf beetle, Oulema melanopus, adult behavioral responses were examined in a Y-tube olfactometer to cis-jasmone induced plant VOC bouquets and to two synthetic blends of VOCs (3 green leaf volatiles (GLVs); 4 terpenes + indole). In both cereals, eight VOCs [(Z)-3-hexanal, (Z)-3-hexanol, (Z)-3-hexanyl acetate, (Z)-ß-ocimene, linalool, ß-caryophyllene, (E)-ß-farnesene, and indole] were induced 100- to 1000-fold after cis-jasmone exposure. The degree of induction in both cereals was usually positively and linearly associated with increasing exposure dose and duration. However, VOC emission rate was only ~2-fold greater from plants exposed to the highest vs. lowest cis-jasmone exposure doses (1 × 10(4) difference) or durations (6-fold difference). Male and female O. melanopus were deterred by both cereal VOC bouquets after plant exposure to the high cis-jasmone dose (1 × 10(4) ng µl(-1)), while females were also deterred after plant exposure to the low dose (1 ng µl(-1)) but attracted to unexposed plant VOC bouquets. Both O. melanopus sexes were repelled by terpene/indole and GLV blends at two concentrations (25 ng · min(-1); 125 ng · min(-1)), but attracted to the lowest dose (1 ng · min(-1)) of a GLV blend. It is possible that the biologically relevant low cis-jasmone dose has ecological activity and potential for inducing field crop VOCs to deter O. melanopus.

Production of phenolics and the emission of volatile organic compounds by perennial ryegrass (Lolium perenne L.)/Neotyphodium lolii association as a response to infection by Fusarium poae.

Grasses very often form symbiotic associations with Neotyphodium/Epichloë endophytic fungi. These endophytes often allow the host grass to be protected from different pathogens. However, there is little known about the mechanisms of such endophyte influence on the host. Thus, the purpose of this research was to examine the effect of the N. lolii endophyte on the total production of phenolic compounds, VOCs emission and the resistance of three perennial ryegrass genotypes infected by pathogenic Fusarium poae. Analyses of total phenolics content were performed in control (not inoculated) and inoculated plants after 1, 2, 3, 4, 5, and 6 days (DAI) and for VOCs after 0, 3, 6 and 12 DAI. The presence of endophytes significantly reduced the disease index in two of the three genotypes relative to that in E-. Plants infected by N. lolii exhibited higher production of phenolics relative to the E- plants. The highest amounts of phenolics were observed on the second and sixth DAI. Genotype Nl22 showed the strongest effect of the endophyte on the production of phenolics, which increased by over 61%. Both the endophyte infected and non-infected plants emitted most abundantly two GLVs ((Z)-3-hexenal, (Z)-3-hexen-1-yl acetate), three terpenes (linalool, (Z)-ocimene, ß-caryophyllene) and three shikimic acid pathway derivatives (benzyl acetate, indole, and methyl salicylate). The endophyte presence and the intervals of VOCs detection were a highly significant source of variation for all emitted volatiles (P<0.001). The genotype of the perennial ryegrass significantly affected only the emission of methyl salicylate (P<0.05) and ß-caryophyllene (P<0.05). Most of the VOCs ((Z)-3-hexen-1-yl acetate, (Z)-3-hexenal, linalool and methyl salicylate) reached their highest levels of emission on the sixth DAI, when averaged over genotypes and endophyte status. The results highlight the role of Neotyphodium spp. in the mediation of quadro-trophic interactions among plants, symbiotic endophytes, invertebrate herbivores and plant pathogenic fungi. Our results also confirm the fact that symbiotic plants can activate a defense reaction faster than non-symbiotic plants after a pathogen attack. Thus, N. lolii can be involved in the defense of perennial ryegrass against pathogens and potentially could be central to the host plants' protection.

Gastrophysa polygoni herbivory on Rumex confertus: single leaf VOC induction and dose dependent herbivore attraction/repellence to individual compounds.

We report large induction (>65(fold) increases) of volatile organic compounds (VOCs) emitted from a single leaf of the invasive weed mossy sorrel, Rumex confertus Willd. (Polygonaceae), by herbivory of the dock leaf beetle, Gastrophysa polygoni L. (Coleoptera: Chrysomelidae). The R. confertus VOC blend induced by G. polygoni herbivory included two green leaf volatiles ((Z)-3-hexenal, (Z)-3-hexen-1-yl acetate) and three terpenes (linalool, ß-caryophyllene, (E)-ß-farnesene). Uninjured leaves produced small constitutive amounts of the GLVs and barely detectable amounts of the terpenes. A Y-tube olfactometer bioassay revealed that both sexes of adult G. polygoni were attracted to (Z)-3-hexenal and (Z)-3-hexen-1-yl acetate at a concentration of 300 ng h(-1). No significant G. polygoni attraction or repellence was detected for any VOC at other concentrations (60 and 1500 ng h(-1)). Yet, G. polygoni males and females were significantly repelled by (or avoided) at the highest test concentration (7500 ng h(-1)) of both GLVs and (E)-ß-farnesene. Mated male and female G. polygoni might be attracted to injured R. confertus leaves, but might avoid R. confertus when VOC concentrations (especially the terpene (E)-ß-farnesene) suggest high overall plant injury from conspecifics, G. viridula, or high infestations of other herbivores that release (E)-ß-farnesene (e.g., aphids). Tests in the future will need to examine G. polygoni responses to VOCs emitted directly from uninjured (constitutive) and injured (induced) R. confertus, and examine whether R. confertus VOC induction concentrations increase with greater tissue removal on a single leaf and/or the number of leaves with feeding injury.

Fusarium infection in maize: volatile induction of infected and neighboring uninfected plants has the potential to attract a pest cereal leaf beetle, Oulema melanopus.

Fusarium infection of maize leaves and/or roots through the soil can stimulate the emission of volatile organic compounds (VOCs). It is also well known that VOC emission from maize plants can repel or attract pests. In our experiments, we studied VOC induction responses of Zea mays L. ssp. mays cv. 'Prosna' having Fusarium infection (mix of four species) in leaves or roots, then tested for VOC induction of uninfected neighboring plants, and finally examined wind-tunnel behavioral responses of the adult cereal leaf beetle, Oulema melanopus L. (Chrysomelidae: Coleoptera) behavior to four induced VOCs. In the first part of our experiment, we confirmed that several green leaf volatiles (GLVs; (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, (Z)-3-hexen-1-yl acetate, 1-hexyl acetate), terpenes (ß-pinene, ß-myrcene, Z-ocimene, linalool, ß-caryophyllene), and shikimic acid pathway derivatives (benzyl acetate, methyl salicylate, indole) were positively induced from maize plants infected by Fusarium spp. The quantities of induced VOCs were higher at 7d than 3d post-infection and greater when plants were infected with Fusarium on leaves rather than through soil. In the second part of our experiment, uninfected maize plants also showed significantly positive induction of several VOCs when neighboring an infected plant where the degree of induction was negatively related to the distance from the infected plant. In the third part of our experiment, a Y-tube bioassay was used to evaluate upwind orientation of adult cereal leaf beetles to four individual VOCs. Female and male O. melanopus were significantly attracted to the GLVs (Z)-3-hexenal and (Z)-3-hexenyl acetate, and the terpenes linalool and ß-caryophyllene. Our results indicate that a pathogen can induce several VOCs in maize plants that also induce VOCs in neighboring uninfected plants, though VOC induction could increase the range at which an insect pest species is attracted to VOC inducing plants.

Cereal crop volatile organic compound induction after mechanical injury, beetle herbivory (Oulema spp.), or fungal infection (Fusarium spp.).

Herbivory, mechanical injury or pathogen infestation to vegetative tissues can induce volatile organic compounds (VOCs) production, which can provide defensive functions to injured and uninjured plants. In our studies with 'McNeal' wheat, 'Otana' oat, and 'Harrington' barley, plants that were mechanically injured, attacked by either of two Oulema spp. (melanopus or cyanella) beetles, or infected by one of the three Fusarium spp. (graminearum, avenaceum, or culmorum), had significant VOC induction compared to undamaged plants. Mechanical injury to the main stem or one leaf caused the induction of one green leaf volatile (GLV) - (Z)-3-hexenol, and three terpenes (ß-linalool, ß-caryophyllene, and α-pinene) with all three grasses; wheat and barley also showed ß-linalool oxide induction. The blend of induced VOCs after Fusarium spp. infestation or Oulema spp. herbivory was dominated by GLVs ((Z)-3-hexenal, (E)-2-hexenal, (E)-2-hexenol, (Z)-3-hexenyl acetate, and 1-hexenyl acetate) and ß-linalool and ß-caryophyllene; beetle herbivory also induced (E)-ß-farnesene. Different ratios of individual VOCs were induced between the two Oulema spp. for each cereal grass and different ratios across the three cereals for each beetle species. Also, different ratios of individual VOCs were induced between the three Fusarium spp. for each cereal grass and different ratios across the three cereals for each fungal pathogen species. Our results are preliminary since we could not simultaneously measure VOC induction from controls with each of the ten different injury treatments for each of the three cereals. However, the comparison of mechanical injury, insect herbivory, and fungal infection has not been previously examined with VOC responses from three different plant species within the same family. Also, our work suggests large qualitative and quantitative overlap of VOC induction from plants of all three cereals having beetle herbivory injury when compared to infection injury from necrotrophic fungal pathogens.

Pulsed odors from maize or spinach elicit orientation in European corn borer neonate larvae.

Lepidoptera larvae are capable of orienting towards or away from plants by using odors as cues but whether this attraction is innate or secondarily acquired remains unknown. We tested the hypothesis that European corn borer (ECB) neonate larvae express an innate attraction towards odors released from maize, and avoidance towards odors from spinach. Neonate larvae were placed on a locomotion compensator within a constant stream of humidified air that was loaded intermittently with airborne odors drawn from potted plants. The odor stream was delivered continuously or pulsed (1 to 10 sec pulses) at 40 ml/min. ECB larvae oriented toward maize odors pulsed at 2 to 6 sec but walked away from maize odors delivered at lower frequencies (9 and 10 sec pulses or to continuous ones). They consistently walked away from spinach odors, irrespective of the pulsing regime except at 1 sec pulses that did not elicit orientation. We further explored odor intensity on orientation towards maize odors by adjusting the odor stream intensity. At higher intensity (60 ml/min), the direction reversal started at the 6 sec half period, while at lower intensity (20 ml/min), it showed up only for the continuous stimulus. ECB larvae exhibit a striking ability to lock on to a direction, which they maintained despite gaps of up to 10 sec in the odor stream. Our results demonstrate that ECB neonate larvae express innate orientation preferences towards natural odors from plants. These reactions correlate well with the biological value of these plants for ECB: maize generally is accepted by ECB larvae and adults, while spinach represents a poor host because it produces (non-volatile) phytoecdysteroids that are toxic and deterrent.