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ABSTRACT Field experiments have demonstrated that wheat mixtures differ in their ability to regulate aphid populations. To further investigate the effectiveness of wheat mixtures (Triticum aestivum and Triticum turgidum) in controlling aphids, we conducted both laboratory and greenhouse experiments. Specifically, we assessed the associational resistance of two wheat mixtures (Florence‐Aurora with Forment, Florence‐Aurora with Montcada), and their respective monocultures, in different stages of the aphid host selection process. We analysed aphid acceptance rate, population growth, and load under different wheat treatments. Additionally, we characterised wheat aboveground biomass and nitrogen content as important functional traits for aphid resistant. Aphid acceptance decreased in plants of cv. Forment when exposed to volatiles from undamaged Florence‐Aurora plants, whereas the other tested combinations tested had no effect. Aphids performed differently in the two mixtures: Florence‐Aurora mixed with Forment significantly reduced aphid population growth and load compared to the monocultures, whereas the combination of Florence‐Aurora with Montcada wheat had no effect on aphid performance. The plant–plant interactions also modified the analysed traits. Nitrogen content of Florence‐Aurora wheat plants was reduced when mixed with Forment wheat, which may explain the lower aphid load observed in plants of cv. Florence‐Aurora when mixed with plants of cv. Forment. However, mixing wheats with similar aboveground biomass resulted in an increase in the average biomass of plants of both cultivars which could have led to a higher aphid population. The data supports the idea of right neighbour, as the benefits of wheat mixtures for aphid control were determined by the identity of the combined plants (or species). Finally, our results suggest that associating wheats with different traits may promote facilitative interactions, which in turn enhances associational resistance, whereas the combination of wheats with similar traits may result in competitive interactions that may hinder aphid control benefits. [ABSTRACT FROM AUTHOR]

Plant volatiles play an important role in intra‐ and interspecific plant communication, inducing direct and indirect defenses against insect pests. However, it remains unknown whether volatile interactions between undamaged cultivars alter host plant volatile emissions and their perception by insect pests. Here, we tested the effects of exposure of a spring barley, Hordeum vulgare L., cultivar, Salome, to volatiles from other cultivars: Fairytale and Anakin. We found that exposing Salome to Fairytale induced a significantly higher emission of trans‐β‐ocimene and two unidentified compounds compared when exposed to Anakin. Aphids were repelled at a higher concentration of trans‐β‐ocimene. Salome exposure to Fairytale had significant repulsive effects on aphid olfactory preference, yet not when Salome was exposed to Anakin. We demonstrate that volatile interactions between specific undamaged plants can induce changes in volatile emission by receiver plants enhancing certain compounds, which can disrupt aphid olfactory preferences. Our results highlight the significant roles of volatiles in plant–plant interactions, affecting plant–insect interactions in suppressing insect pests. This has important implications for crop protection and sustainable agriculture. Summary statement: The airborne interactions between certain undamaged spring barley (Hordeum vulgare L.) cultivars induce changes in volatile emission in receiving plants by enhancing the production of certain ideal volatile organic compounds. These changes trigger strong repellent effects on aphids (Rhopalosiphum padi L.), suggesting the significant roles of volatile‐mediated plant–plant interactions in the development of integrated pest management for sustainable agriculture practices. [ABSTRACT FROM AUTHOR]

The effect of cultivar mixtures on aphid control is attributed to the masking or alteration of host-preferred cultivar odor cues. However, the underlying physiological mechanism remains unclear. This study assessed alterations in the volatile emissions of wheat cultivars grown together (Florence-Aurora and Forment; Florence-Aurora and Montcada) and the consequences for the olfactory preference of aphids. Volatile organic compounds were collected from wheat plants grown in a laboratory under mixed or monoculture conditions and subsequently analyzed. The odor profiles of Florence-Aurora and Montcada were indistinguishable from each other. However, the odors of Florence-Aurora and Forment grown in monocultures differed significantly from those emitted by their mixture. The Florence-Aurora and Forment mixture induced plant physiological responses that affected the emission of single volatile compounds and, consequently, altered volatile organic compound ratios. English grain aphids (Sitobion avenae) were less attracted to the odors of Florence-Aurora and Forment when grown as a mixture than the combination of the odors from Florence-Aurora and Forment monocultures. Moreover, aphids preferred clean air over the odor from the Florence-Aurora and Forment mixture but preferred the odor from the Florence-Aurora and Montcada mixture over clean air. This study highlights the beneficial effects of intraspecific plant diversity on aphid control by altering plant odors in response to plant-plant interactions. The emission of less attractive odor cues consequently affects plant-aphid interactions; hence, less attractive odors are likely to impair aphid host-locating behavior. This effect was exclusive to certain cultivar mixtures, which supports the "right neighbor" concept. [ABSTRACT FROM AUTHOR]

The impact of climate change drivers on cultivated plants and pest insects has come into research focus. One of the most significant drivers is atmospheric carbon dioxide, which is converted into primary plant metabolites by photosynthesis. Increased atmospheric CO2 concentrations therefore affect plant chemistry. The chemical composition of non-volatile and volatile organic compounds of plants is used by insects to locate and identify suitable host plants for feeding and reproduction. We investigated whether elevated CO2 concentrations in the atmosphere affect the plant-pest interaction in a fruit crop of high economic importance in Europe. Therefore, potted pear trees were cultivated under specified CO2 conditions in a Free-Air Carbon dioxide Enrichment (FACE) facility at Geisenheim University in Germany for up to 14 weeks, beginning from bud swelling. We compared emitted volatiles from these pear trees cultivated for 7 and 14 weeks under two different CO2 levels (ambient: ca. 400 ppm and elevated: ca. 450 ppm CO2) and their impact on pest insect behavior. In total, we detected and analyzed 76 VOCs from pear trees. While we did not detect an overall change in VOC compositions, the relative release of single compounds changed in response to CO2 increase. Differences in VOC release were inconsistent over time (phenology stages) and between study years, indicating interactions with other climate parameters, such as temperature. Even though insect-plant interaction can rely on specific volatile compounds and specific mixtures of compounds, respectively, the changes of VOC patterns in our field study did not impact the host choice behavior of C. pyri females. In olfactometer trials, 64% and 60% of the females preferred the odor of pear trees cultivated under elevated CO2 for 7 and 14 weeks, respectively, over the odor from pear trees cultivated under ambient CO2. In binary-choice oviposition assays, C. pyri females laid most eggs on pears during April 2020; on average, 51.9 (± 51.3) eggs were laid on pears cultivated under eCO2 and 60.3 (± 48.7) eggs on aCO2. [ABSTRACT FROM AUTHOR]

Phytopathogens are responsible for devastating plant diseases threatening agriculture and food security worldwide. Phloem-restricted bacterial plant pathogens belonging to the classes mollicutes (‘Candidatus Phytoplasma’, Spiroplasma), α-proteobacteria, and γ-proteobacteria have a significant impact on several high-value crops. These bacteria are obligate parasites, depending on their plant and insect hosts. Inside the plants, they are restricted to the phloem, which is a source of primary and secondary plant metabolites representing a suitable niche for them. Additionally, phloem sap is utilized for nutrition by multiple Hemipterans and several species within the leafhopper, planthopper, and psyllid taxa, which can acquire and transmit the phloem-dwelling bacteria during feeding. The present review aims at providing an overview of interactions between phloem-restricted bacterial plant pathogens and their vector insects, which are mediated by primary and secondary plant metabolites. The overview is organized in two sections describing the current knowledge of phloem and volatile metabolite mediated interactions between pathogens, their host plants, their vector insects, and where information is available, the antagonists of vectors. This bibliographic oriented part is followed by a comprehensive synthesis of the reviewed literature and important research gaps were identified. The evolution of plant – pathogen – vector systems and novel trends on pest management strategies of phloemrestricted bacteria, in which semiochemicals are applied, are discussed. Finally, an outlook on future prospects is given. [ABSTRACT FROM AUTHOR]

To study inheritance of Malus sieboldii-derived apple proliferation resistance, 14 cross combinations were performed with the tetraploid apomictic M. sieboldii and first and second generation parental lines as donor of resistance and Malus x domestica scion cultivars and apple rootstocks as donor of pomological traits. In the progeny examined mainly three classes were present consisting of mother-like plants with the allele composition of the maternal apomict (ML), hybrids based on fertilization of an unreduced egg cell (hybrid I), and fully recombinant plants (hybrid II). Two-year screening of inoculated plants in the nursery revealed that progeny classes ML and H I responded similarly to infection and that about half of the progeny showed satisfactory resistance. No appropriate resistance was identified in progeny class H II. This might be due to the fact that in fully recombinant offspring M. sieboldii haplotypes have been reduced from 4n to 1-2n or were entirely lost. Following nursery-growing, promising trees were evaluated for six more years in the orchard. Nearly all of them showed satisfactory resistance but were mostly less productive and more vigorous than trees on clonal standard rootstock M9. However, mainly among the offspring of progeny 4608 × M9, resistant genotypes were identified showing pomological properties similar to M9. [ABSTRACT FROM AUTHOR]

Plant sap feeding insects like psyllids are known to be vectors of phloem dwelling bacteria ('Candidatus Phytoplasma' and 'Ca. Liberibacter'), plant pathogens which cause severe diseases and economically important crop damage. Some univoltine psyllid species have a particular life cycle, within one generation they alternate two times between different host plant species. The plum psyllid Cacopsylla pruni, the vector of European Stone Fruit Yellows (ESFY), one of the most serious pests in European fruit production, migrates to stone fruit orchards (Prunus spp.) for mating and oviposition in early spring. The young adults of the new generation leave the Prunus trees in summer and emigrate to their overwintering hosts like spruce and other conifers. Very little is known about the factors responsible for the regulation of migration, reasons for host alternation, and the behavior of psyllids during their phase of life on conifers. Because insect feeding behavior and host acceptance is driven by different biotic factors, such as olfactory and gustatory cues as well as mechanical barriers, we carried out electrical penetration graph (EPG) recordings and survival bioassays with C. pruni on different conifer species as potential overwintering hosts and analyzed the chemical composition of the respective plant saps. We are the first to show that migrating psyllids do feed on overwintering hosts and that nymphs are able to ingest phloem and xylem sap of coniferous trees, but cannot develop on conifer diet. Analyses of plant saps reveal qualitative differences in the chemical composition between coniferous trees and Prunus as well as within conifer species. These differences are discussed with regard to nutritional needs of psyllid nymphs for proper development, overwintering needs of adults and restriction of'Ca. P. prunorum' to Prunus phloem. [ABSTRACT FROM AUTHOR]

The article reports on developing strategies for preventing European Stone Fruit Yellows (ESFY), one of the most serious diseases in European fruit production. It is said that a specialized bacterium located in the phloem tissue of Prunus ssp., the Phytoplasma "Candidatus Phytoplasma prunorum," causes ESFY.

In this chapter, we give an introduction to innovative attempts for the collection, identification, and statistical analysis of volatile organic compound (VOC) patterns emitted by phytoplasma-infected plants compared to healthy plants by the use of state-of-the-art techniques. This encompasses headspace-sampling techniques, gas chromatography coupled with mass spectrometry, and identification of VOC patterns by the "Automated Mass Spectral Deconvolution and Identification System" (AMDIS) followed by appropriate statistical analysis.